making a variable mutable

exercises/variables/variables3.rs

@@ -1,7 +1,7 @@
 // variables3.rs
 // Execute `rustlings hint variables3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
+
 
 fn main() {
     let x: i32 = 10;

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);