diff --git a/exercises/enums/enums1.rs b/exercises/enums/enums1.rs
index 511ba740e2..535d21e1ce 100644
--- a/exercises/enums/enums1.rs
+++ b/exercises/enums/enums1.rs
@@ -1,11 +1,13 @@
 // enums1.rs
 // No hints this time! ;)
 
-// I AM NOT DONE
 
 #[derive(Debug)]
 enum Message {
-    // TODO: define a few types of messages as used below
+    Quit,
+    Echo,
+    Move,
+    ChangeColor
 }
 
 fn main() {
diff --git a/exercises/enums/enums2.rs b/exercises/enums/enums2.rs
index 18479f874d..5a58a2f108 100644
--- a/exercises/enums/enums2.rs
+++ b/exercises/enums/enums2.rs
@@ -1,11 +1,13 @@
 // enums2.rs
 // Execute `rustlings hint enums2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 #[derive(Debug)]
 enum Message {
-    // TODO: define the different variants used below
+    Move {x: i32, y: i32},
+    Echo(String),
+    ChangeColor(i32, i32, i32),
+    Quit
 }
 
 impl Message {
diff --git a/exercises/enums/enums3.rs b/exercises/enums/enums3.rs
index 55acf6bc9d..54b9d225ce 100644
--- a/exercises/enums/enums3.rs
+++ b/exercises/enums/enums3.rs
@@ -2,10 +2,12 @@
 // Address all the TODOs to make the tests pass!
 // Execute `rustlings hint enums3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 enum Message {
-    // TODO: implement the message variant types based on their usage below
+    ChangeColor((u8, u8, u8)),
+    Echo(String),
+    Move(Point),
+    Quit
 }
 
 struct Point {
@@ -37,7 +39,12 @@ impl State {
     }
 
     fn process(&mut self, message: Message) {
-        // TODO: create a match expression to process the different message variants
+        match message {
+            Message::ChangeColor(color) => self.change_color(color),
+            Message::Echo(string) => self.echo(string),
+            Message::Move(position) => self.move_position(position),
+            Message::Quit => self.quit()
+        }
     }
 }
 
diff --git a/exercises/error_handling/errors1.rs b/exercises/error_handling/errors1.rs
index bcee9723e9..6aaef210ab 100644
--- a/exercises/error_handling/errors1.rs
+++ b/exercises/error_handling/errors1.rs
@@ -5,14 +5,13 @@
 // construct to `Option` that can be used to express error conditions. Let's use it!
 // Execute `rustlings hint errors1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
-pub fn generate_nametag_text(name: String) -> Option<String> {
+
+pub fn generate_nametag_text(name: String) -> Result<String, String> {
     if name.is_empty() {
-        // Empty names aren't allowed.
-        None
+        Err("`name` was empty; it must be nonempty.".into())
     } else {
-        Some(format!("Hi! My name is {}", name))
+        Ok(format!("Hi! My name is {}", name))
     }
 }
 
diff --git a/exercises/error_handling/errors2.rs b/exercises/error_handling/errors2.rs
index 1cd8fc66b0..35e090c59d 100644
--- a/exercises/error_handling/errors2.rs
+++ b/exercises/error_handling/errors2.rs
@@ -17,16 +17,17 @@
 // one is a lot shorter!
 // Execute `rustlings hint errors2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
     let processing_fee = 1;
     let cost_per_item = 5;
     let qty = item_quantity.parse::<i32>();
-
-    Ok(qty * cost_per_item + processing_fee)
+    match qty 
+    {
+        Ok(value) => Ok(value * cost_per_item + processing_fee), _ => qty
+    }
+    
 }
 
 #[cfg(test)]
diff --git a/exercises/error_handling/errors3.rs b/exercises/error_handling/errors3.rs
index a2d2d1901d..c9784e3d54 100644
--- a/exercises/error_handling/errors3.rs
+++ b/exercises/error_handling/errors3.rs
@@ -4,11 +4,9 @@
 // Why not? What should we do to fix it?
 // Execute `rustlings hint errors3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
-fn main() {
+fn main() -> Result<(), ParseIntError> {
     let mut tokens = 100;
     let pretend_user_input = "8";
 
@@ -20,6 +18,7 @@ fn main() {
         tokens -= cost;
         println!("You now have {} tokens.", tokens);
     }
+    Ok(())
 }
 
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
diff --git a/exercises/error_handling/errors4.rs b/exercises/error_handling/errors4.rs
index 0efe8ccd5a..fade9f4f2f 100644
--- a/exercises/error_handling/errors4.rs
+++ b/exercises/error_handling/errors4.rs
@@ -1,7 +1,6 @@
 // errors4.rs
 // Execute `rustlings hint errors4` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 #[derive(PartialEq, Debug)]
 struct PositiveNonzeroInteger(u64);
@@ -14,7 +13,11 @@ enum CreationError {
 
 impl PositiveNonzeroInteger {
     fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
-        // Hmm...? Why is this only returning an Ok value?
+        if value < 0 {
+            return Err(CreationError::Negative)
+        } else if value == 0 {
+            return Err(CreationError::Zero)
+        }
         Ok(PositiveNonzeroInteger(value as u64))
     }
 }
diff --git a/exercises/error_handling/errors5.rs b/exercises/error_handling/errors5.rs
index 2ba8f9039d..f31e13f51e 100644
--- a/exercises/error_handling/errors5.rs
+++ b/exercises/error_handling/errors5.rs
@@ -23,7 +23,7 @@ use std::fmt;
 use std::num::ParseIntError;
 
 // TODO: update the return type of `main()` to make this compile.
-fn main() -> Result<(), Box<dyn ???>> {
+fn main() -> Result<(), Box<dyn error::Error>> {
     let pretend_user_input = "42";
     let x: i64 = pretend_user_input.parse()?;
     println!("output={:?}", PositiveNonzeroInteger::new(x)?);
diff --git a/exercises/error_handling/errors6.rs b/exercises/error_handling/errors6.rs
index 1306fb03e1..7ee3d2deba 100644
--- a/exercises/error_handling/errors6.rs
+++ b/exercises/error_handling/errors6.rs
@@ -23,16 +23,16 @@ impl ParsePosNonzeroError {
     fn from_creation(err: CreationError) -> ParsePosNonzeroError {
         ParsePosNonzeroError::Creation(err)
     }
-    // TODO: add another error conversion function here.
-    // fn from_parseint...
+    
+    fn from_parseint(err: ParseIntError) -> ParsePosNonzeroError {
+        ParsePosNonzeroError::ParseInt(err)
+    }
 }
 
 fn parse_pos_nonzero(s: &str)
     -> Result<PositiveNonzeroInteger, ParsePosNonzeroError>
 {
-    // TODO: change this to return an appropriate error instead of panicking
-    // when `parse()` returns an error.
-    let x: i64 = s.parse().unwrap();
+    let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
     PositiveNonzeroInteger::new(x)
         .map_err(ParsePosNonzeroError::from_creation)
 }
diff --git a/exercises/intro/intro2.rs b/exercises/intro/intro2.rs
index efc1af2059..7ba39ca86c 100644
--- a/exercises/intro/intro2.rs
+++ b/exercises/intro/intro2.rs
@@ -2,8 +2,7 @@
 // Make the code print a greeting to the world.
 // Execute `rustlings hint intro2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 fn main() {
-    println!("Hello {}!");
+    let greeting = "World";
+    println!("Hello {}!", greeting);
 }
diff --git a/exercises/move_semantics/move_semantics1.rs b/exercises/move_semantics/move_semantics1.rs
index aac6dfc39c..a636de7d24 100644
--- a/exercises/move_semantics/move_semantics1.rs
+++ b/exercises/move_semantics/move_semantics1.rs
@@ -6,7 +6,7 @@
 fn main() {
     let vec0 = Vec::new();
 
-    let vec1 = fill_vec(vec0);
+    let mut vec1 = fill_vec(vec0);
 
     println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 
diff --git a/exercises/move_semantics/move_semantics2.rs b/exercises/move_semantics/move_semantics2.rs
index 64870850ec..db66c01adf 100644
--- a/exercises/move_semantics/move_semantics2.rs
+++ b/exercises/move_semantics/move_semantics2.rs
@@ -7,7 +7,7 @@
 fn main() {
     let vec0 = Vec::new();
 
-    let mut vec1 = fill_vec(vec0);
+    let mut vec1 = fill_vec(&vec0);
 
     // Do not change the following line!
     println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);
@@ -17,8 +17,8 @@ fn main() {
     println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 }
 
-fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
-    let mut vec = vec;
+fn fill_vec(vec: &Vec<i32>) -> Vec<i32> {
+    let mut vec = vec.to_vec();
 
     vec.push(22);
     vec.push(44);
diff --git a/exercises/move_semantics/move_semantics3.rs b/exercises/move_semantics/move_semantics3.rs
index eaa30e3344..b5e4db2967 100644
--- a/exercises/move_semantics/move_semantics3.rs
+++ b/exercises/move_semantics/move_semantics3.rs
@@ -17,7 +17,7 @@ fn main() {
     println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 }
 
-fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+fn fill_vec(mut vec: Vec<i32>) -> Vec<i32> {
     vec.push(22);
     vec.push(44);
     vec.push(66);
diff --git a/exercises/move_semantics/move_semantics4.rs b/exercises/move_semantics/move_semantics4.rs
index 99834ec34e..99130074ec 100644
--- a/exercises/move_semantics/move_semantics4.rs
+++ b/exercises/move_semantics/move_semantics4.rs
@@ -7,9 +7,8 @@
 // I AM NOT DONE
 
 fn main() {
-    let vec0 = Vec::new();
 
-    let mut vec1 = fill_vec(vec0);
+    let mut vec1 = fill_vec();
 
     println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 
@@ -20,7 +19,7 @@ fn main() {
 
 // `fill_vec()` no longer takes `vec: Vec<i32>` as argument
 fn fill_vec() -> Vec<i32> {
-    let mut vec = vec;
+    let mut vec = Vec::new();
 
     vec.push(22);
     vec.push(44);
diff --git a/exercises/move_semantics/move_semantics5.rs b/exercises/move_semantics/move_semantics5.rs
index 36eae127ac..d25a01153e 100644
--- a/exercises/move_semantics/move_semantics5.rs
+++ b/exercises/move_semantics/move_semantics5.rs
@@ -8,8 +8,9 @@
 fn main() {
     let mut x = 100;
     let y = &mut x;
-    let z = &mut x;
     *y += 100;
+    let z = &mut x;
+
     *z += 1000;
     assert_eq!(x, 1200);
 }
diff --git a/exercises/move_semantics/move_semantics6.rs b/exercises/move_semantics/move_semantics6.rs
index eb52a848d3..f8cef7f0d4 100644
--- a/exercises/move_semantics/move_semantics6.rs
+++ b/exercises/move_semantics/move_semantics6.rs
@@ -7,19 +7,19 @@
 fn main() {
     let data = "Rust is great!".to_string();
 
-    get_char(data);
+    get_char(&data);
 
-    string_uppercase(&data);
+    string_uppercase(data);
 }
 
 // Should not take ownership
-fn get_char(data: String) -> char {
+fn get_char(data: &str) -> char {
     data.chars().last().unwrap()
 }
 
 // Should take ownership
-fn string_uppercase(mut data: &String) {
-    data = &data.to_uppercase();
+fn string_uppercase(mut data: String) {
+    data = data.to_uppercase();
 
     println!("{}", data);
 }
diff --git a/exercises/standard_library_types/arc1.rs b/exercises/standard_library_types/arc1.rs
index 93a27036f2..80cede2c9d 100644
--- a/exercises/standard_library_types/arc1.rs
+++ b/exercises/standard_library_types/arc1.rs
@@ -18,7 +18,6 @@
 // where the second TODO comment is. Try not to create any copies of the `numbers` Vec!
 // Execute `rustlings hint arc1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 #![forbid(unused_imports)] // Do not change this, (or the next) line.
 use std::sync::Arc;
@@ -26,11 +25,11 @@ use std::thread;
 
 fn main() {
     let numbers: Vec<_> = (0..100u32).collect();
-    let shared_numbers = // TODO
+    let shared_numbers = Arc::new(numbers);
     let mut joinhandles = Vec::new();
 
     for offset in 0..8 {
-        let child_numbers = // TODO
+        let child_numbers = shared_numbers.clone();
         joinhandles.push(thread::spawn(move || {
             let sum: u32 = child_numbers.iter().filter(|n| *n % 8 == offset).sum();
             println!("Sum of offset {} is {}", offset, sum);
diff --git a/exercises/strings/strings1.rs b/exercises/strings/strings1.rs
index 0de86a1dbf..d89d2b0e9c 100644
--- a/exercises/strings/strings1.rs
+++ b/exercises/strings/strings1.rs
@@ -2,13 +2,11 @@
 // Make me compile without changing the function signature!
 // Execute `rustlings hint strings1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 fn main() {
     let answer = current_favorite_color();
     println!("My current favorite color is {}", answer);
 }
 
 fn current_favorite_color() -> String {
-    "blue"
+    return "blue".to_string();
 }
diff --git a/exercises/strings/strings2.rs b/exercises/strings/strings2.rs
index 0c48ec959d..26c2547663 100644
--- a/exercises/strings/strings2.rs
+++ b/exercises/strings/strings2.rs
@@ -2,8 +2,6 @@
 // Make me compile without changing the function signature!
 // Execute `rustlings hint strings2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 fn main() {
     let word = String::from("green"); // Try not changing this line :)
     if is_a_color_word(word) {
@@ -13,6 +11,6 @@ fn main() {
     }
 }
 
-fn is_a_color_word(attempt: &str) -> bool {
+fn is_a_color_word(attempt: String) -> bool {
     attempt == "green" || attempt == "blue" || attempt == "red"
 }
diff --git a/exercises/strings/strings3.rs b/exercises/strings/strings3.rs
index e2353aecc9..610e3d1938 100644
--- a/exercises/strings/strings3.rs
+++ b/exercises/strings/strings3.rs
@@ -1,21 +1,16 @@
 // strings3.rs
 // Execute `rustlings hint strings3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 fn trim_me(input: &str) -> String {
-    // TODO: Remove whitespace from both ends of a string!
-    ???
+    return input.trim().to_string();
 }
 
-fn compose_me(input: &str) -> String {
-    // TODO: Add " world!" to the string! There's multiple ways to do this!
-    ???
+fn compose_me(input: &str) -> String {    
+    return input.to_string() + " world!";
 }
 
 fn replace_me(input: &str) -> String {
-    // TODO: Replace "cars" in the string with "balloons"!
-    ???
+    return input.replace("cars", "balloons");
 }
 
 #[cfg(test)]
diff --git a/exercises/strings/strings4.rs b/exercises/strings/strings4.rs
index c410b56252..c5caaf8bdb 100644
--- a/exercises/strings/strings4.rs
+++ b/exercises/strings/strings4.rs
@@ -6,8 +6,6 @@
 // before the parentheses on each line. If you're right, it will compile!
 // No hints this time!
 
-// I AM NOT DONE
-
 fn string_slice(arg: &str) {
     println!("{}", arg);
 }
@@ -16,14 +14,14 @@ fn string(arg: String) {
 }
 
 fn main() {
-    ???("blue");
-    ???("red".to_string());
-    ???(String::from("hi"));
-    ???("rust is fun!".to_owned());
-    ???("nice weather".into());
-    ???(format!("Interpolation {}", "Station"));
-    ???(&String::from("abc")[0..1]);
-    ???("  hello there ".trim());
-    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
-    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
+    string_slice("blue");
+    string("red".to_string());
+    string(String::from("hi"));
+    string("rust is fun!".to_owned());
+    string_slice("nice weather".into());
+    string(format!("Interpolation {}", "Station"));
+    string_slice(&String::from("abc")[0..1]);
+    string_slice("  hello there ".trim());
+    string("Happy Monday!".to_string().replace("Mon", "Tues"));
+    string("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }
diff --git a/exercises/structs/structs3.rs b/exercises/structs/structs3.rs
index 3536a4573e..9ede201de2 100644
--- a/exercises/structs/structs3.rs
+++ b/exercises/structs/structs3.rs
@@ -26,12 +26,12 @@ impl Package {
         }
     }
 
-    fn is_international(&self) -> ??? {
-        // Something goes here...
+    fn is_international(&self) -> bool {
+        self.sender_country != self.recipient_country
     }
 
-    fn get_fees(&self, cents_per_gram: i32) -> ??? {
-        // Something goes here...
+    fn get_fees(&self, cents_per_gram: i32) -> i32 {
+        self.weight_in_grams * cents_per_gram 
     }
 }
 
diff --git a/exercises/tests/tests1.rs b/exercises/tests/tests1.rs
index 8b6ea37469..3563e8e7fe 100644
--- a/exercises/tests/tests1.rs
+++ b/exercises/tests/tests1.rs
@@ -7,12 +7,12 @@
 // pass! Make the test fail!
 // Execute `rustlings hint tests1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 #[cfg(test)]
 mod tests {
     #[test]
     fn you_can_assert() {
-        assert!();
+        let x = 1;
+        assert!(x != 1);
     }
 }
diff --git a/exercises/tests/tests2.rs b/exercises/tests/tests2.rs
index a5ac15b11f..69e79ebbe0 100644
--- a/exercises/tests/tests2.rs
+++ b/exercises/tests/tests2.rs
@@ -3,12 +3,10 @@
 // pass! Make the test fail!
 // Execute `rustlings hint tests2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 #[cfg(test)]
 mod tests {
     #[test]
     fn you_can_assert_eq() {
-        assert_eq!();
+        assert_eq!(1, 2);
     }
 }
diff --git a/exercises/tests/tests3.rs b/exercises/tests/tests3.rs
index 196a81a0e5..28b0ebe036 100644
--- a/exercises/tests/tests3.rs
+++ b/exercises/tests/tests3.rs
@@ -4,8 +4,6 @@
 // we expect to get when we call `is_even(5)`.
 // Execute `rustlings hint tests3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 pub fn is_even(num: i32) -> bool {
     num % 2 == 0
 }
@@ -16,11 +14,11 @@ mod tests {
 
     #[test]
     fn is_true_when_even() {
-        assert!();
+        assert!(is_even(6));
     }
 
     #[test]
     fn is_false_when_odd() {
-        assert!();
+        assert!(!is_even(5));
     }
 }
diff --git a/exercises/variables/variables1.rs b/exercises/variables/variables1.rs
index f4d182accf..b0ad72daf7 100644
--- a/exercises/variables/variables1.rs
+++ b/exercises/variables/variables1.rs
@@ -2,9 +2,8 @@
 // Make me compile!
 // Execute `rustlings hint variables1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 fn main() {
-    x = 5;
+    let x = 5;
     println!("x has the value {}", x);
 }
diff --git a/exercises/variables/variables2.rs b/exercises/variables/variables2.rs
index 641aeb8e09..c4a5832d5f 100644
--- a/exercises/variables/variables2.rs
+++ b/exercises/variables/variables2.rs
@@ -1,10 +1,9 @@
 // variables2.rs
 // Execute `rustlings hint variables2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
 
 fn main() {
-    let x;
+    let x = 10;
     if x == 10 {
         println!("x is ten!");
     } else {
diff --git a/exercises/variables/variables3.rs b/exercises/variables/variables3.rs
index 819b1bc791..b525f39715 100644
--- a/exercises/variables/variables3.rs
+++ b/exercises/variables/variables3.rs
@@ -4,6 +4,6 @@
 // I AM NOT DONE
 
 fn main() {
-    let x: i32;
+    let x = 1;
     println!("Number {}", x);
 }
diff --git a/exercises/variables/variables4.rs b/exercises/variables/variables4.rs
index 54491b0a20..ae3d20e9fd 100644
--- a/exercises/variables/variables4.rs
+++ b/exercises/variables/variables4.rs
@@ -4,7 +4,7 @@
 // I AM NOT DONE
 
 fn main() {
-    let x = 3;
+    let mut x = 3;
     println!("Number {}", x);
     x = 5; // don't change this line
     println!("Number {}", x);
diff --git a/exercises/variables/variables5.rs b/exercises/variables/variables5.rs
index 0e670d2afe..65faf126f8 100644
--- a/exercises/variables/variables5.rs
+++ b/exercises/variables/variables5.rs
@@ -6,6 +6,6 @@
 fn main() {
     let number = "T-H-R-E-E"; // don't change this line
     println!("Spell a Number : {}", number);
-    number = 3; // don't rename this variable
+    let number = 3; // don't rename this variable
     println!("Number plus two is : {}", number + 2);
 }
diff --git a/exercises/variables/variables6.rs b/exercises/variables/variables6.rs
index a8520122c5..efd36bdfc9 100644
--- a/exercises/variables/variables6.rs
+++ b/exercises/variables/variables6.rs
@@ -3,7 +3,7 @@
 
 // I AM NOT DONE
 
-const NUMBER = 3;
+const NUMBER: u32 = 3;
 fn main() {
     println!("Number {}", NUMBER);
 }