progress variables

exercises/01_variables/variables5.rs

@@ -3,6 +3,6 @@ fn main() {
     println!("Spell a number: {number}");
 
     // TODO: Fix the compiler error by changing the line below without renaming the variable.
-    number = 3;
+    let mut number = 3;
     println!("Number plus two is: {}", number + 2);
 }