In terms of how the Javascript interpreter works, yes, it's a good idea to put semicolons where they can be used in order to prevent interpreter look-ahead when not necessary.

In this case, it's basically telling the interpreter "no, there's nothing more coming after this for this assignment". I mostly do it out of habit now after watching a Crockford Google talk some time ago.

Well, unless you look carefully at the expected output.. If you're like me though, you tend to speed read through the description ;)

Watch for whitespace. The instructions (and the resulting error) aren't very clear.