This problem gave my younger son a bit of difficulty today. There are a couple of ideas in this problem that require you to be careful with your counting.

This problem required you to keep track of a few different geometric ideas and a few algebra / arithmetic ideas in order to get to the solution. No one of those ideas alone is super tough, but all of them together really require you to work carefully.

I really liked how these two problems required the kids to work carefully. That careful work makes getting to the solution really satisfying!