X = 9 . to find this out, you need to plug in the given info into a^2 + b^2 = c^2 .. so we have a^2 + 6^2 = 117. Which is a^2 + 36 = 117. so we need to get a by itself. to do so, subtract 36 from both sides to get a^2 = 81. Lastly, we need to find the square root of both sides. the square root of a^2 is a, and the square root of 81 is 9. which leaves us with a = 9