Mental math it, man. It's not that hard. You passed elementary school, so you should know your squares up to 100 pretty well, right? Well, what's the square root of 61? It's closer to 64 than 49, so the root is probably more towards 8. They won't dick you and give you, like, 7.6, 7.7, 7.8, and 7.9 as answer choices.