Saw this problem posted on twitter by James Cleveland:
I thought it would make a nice problem for the boys to talk through. It was actually much better than I expected from the point of view of hearing kids talk about math.
So, without much comment, here are their thoughts. My 6th grader first and then my 4th grader. Probably the most difficult piece for both kids was figuring out that the two solutions they found were, in fact, the only two solutions.