diff --git a/exercises/20_threads/threads1.rs b/exercises/20_threads/threads1.rs
index 80b6def3..5dbfb9c7 100644
--- a/exercises/20_threads/threads1.rs
+++ b/exercises/20_threads/threads1.rs
@@ -8,7 +8,6 @@
 // Execute `rustlings hint threads1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 use std::thread;
 use std::time::{Duration, Instant};
@@ -27,6 +26,7 @@ fn main() {
     let mut results: Vec<u128> = vec![];
     for handle in handles {
         // TODO: a struct is returned from thread::spawn, can you use it?
+        results.push(handle.join().unwrap());
     }
 
     if results.len() != 10 {
diff --git a/exercises/20_threads/threads2.rs b/exercises/20_threads/threads2.rs
index 62dad80d..6b85606c 100644
--- a/exercises/20_threads/threads2.rs
+++ b/exercises/20_threads/threads2.rs
@@ -7,9 +7,8 @@
 // Execute `rustlings hint threads2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
-use std::sync::Arc;
+use std::sync::{Arc, Mutex};
 use std::thread;
 use std::time::Duration;
 
@@ -18,14 +17,14 @@ struct JobStatus {
 }
 
 fn main() {
-    let status = Arc::new(JobStatus { jobs_completed: 0 });
+    let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));
     let mut handles = vec![];
     for _ in 0..10 {
         let status_shared = Arc::clone(&status);
         let handle = thread::spawn(move || {
             thread::sleep(Duration::from_millis(250));
             // TODO: You must take an action before you update a shared value
-            status_shared.jobs_completed += 1;
+            status_shared.lock().unwrap().jobs_completed += 1;
         });
         handles.push(handle);
     }
@@ -34,6 +33,6 @@ fn main() {
         // TODO: Print the value of the JobStatus.jobs_completed. Did you notice
         // anything interesting in the output? Do you have to 'join' on all the
         // handles?
-        println!("jobs completed {}", ???);
+        println!("jobs completed {}", status.lock().unwrap().jobs_completed);
     }
 }
diff --git a/exercises/20_threads/threads3.rs b/exercises/20_threads/threads3.rs
index 91006bbc..8de76d7c 100644
--- a/exercises/20_threads/threads3.rs
+++ b/exercises/20_threads/threads3.rs
@@ -3,7 +3,6 @@
 // Execute `rustlings hint threads3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 use std::sync::mpsc;
 use std::sync::Arc;
@@ -30,11 +29,12 @@ fn send_tx(q: Queue, tx: mpsc::Sender<u32>) -> () {
     let qc = Arc::new(q);
     let qc1 = Arc::clone(&qc);
     let qc2 = Arc::clone(&qc);
+    let tx1 = tx.clone();
 
     thread::spawn(move || {
         for val in &qc1.first_half {
             println!("sending {:?}", val);
-            tx.send(*val).unwrap();
+            tx1.send(*val).unwrap();
             thread::sleep(Duration::from_secs(1));
         }
     });
diff --git a/exercises/21_macros/macros1.rs b/exercises/21_macros/macros1.rs
index 678de6ee..87319302 100644
--- a/exercises/21_macros/macros1.rs
+++ b/exercises/21_macros/macros1.rs
@@ -3,7 +3,6 @@
 // Execute `rustlings hint macros1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 macro_rules! my_macro {
     () => {
@@ -12,5 +11,5 @@ macro_rules! my_macro {
 }
 
 fn main() {
-    my_macro();
+    my_macro!();
 }
diff --git a/exercises/21_macros/macros2.rs b/exercises/21_macros/macros2.rs
index 788fc16a..d558c971 100644
--- a/exercises/21_macros/macros2.rs
+++ b/exercises/21_macros/macros2.rs
@@ -3,14 +3,14 @@
 // Execute `rustlings hint macros2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
-fn main() {
-    my_macro!();
-}
 
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");
     };
 }
+fn main() {
+    my_macro!();
+}
+
+
diff --git a/exercises/21_macros/macros3.rs b/exercises/21_macros/macros3.rs
index b795c149..345b46a7 100644
--- a/exercises/21_macros/macros3.rs
+++ b/exercises/21_macros/macros3.rs
@@ -5,9 +5,9 @@
 // Execute `rustlings hint macros3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 mod macros {
+    #[macro_export]
     macro_rules! my_macro {
         () => {
             println!("Check out my macro!");
diff --git a/exercises/21_macros/macros4.rs b/exercises/21_macros/macros4.rs
index 71b45a09..d8ed2c5b 100644
--- a/exercises/21_macros/macros4.rs
+++ b/exercises/21_macros/macros4.rs
@@ -3,16 +3,15 @@
 // Execute `rustlings hint macros4` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 #[rustfmt::skip]
 macro_rules! my_macro {
     () => {
         println!("Check out my macro!");
-    }
+    };
     ($val:expr) => {
         println!("Look at this other macro: {}", $val);
-    }
+    };
 }
 
 fn main() {