I don't give them the answer, someone has to get it. Sometimes this takes until later in the lesson and I just wait. There is always someone who wants to get it bad enough to keep at it. Here's the answer
This problem requires you to think outside the box, literally and figuratively. I like to try to get them to realize that the fun of math is in the ah-ha moment, not just repeating what I say, and I think this problem is good for that.