Update 4.iterations.md

while

docs/4.iterations.md

@@ -153,7 +153,7 @@ We constructed a loop to multiply each number by 2, but we only have 1 number as
         }
         ```
 
-    In lines 19 to 23, we applied a `while` loop to ensure that `collatz()` continues to be applied until `x == 1`, which marks the end of the loop. 
+    In lines 17 to 21, we applied a `while` loop to ensure that `collatz()` continues to be applied until `x == 1`, which marks the end of the loop. 
 
 ## The `map()` family