The answer is x=10.295 roughly. You get this by using Pythagorean theorem, a^2 + b^2 = c^2. You just plug in the numbers to get the last side, 9^2 + 5^2 = c^2 and solve. 81 + 25 = c^2, 106 = c^2, then you take the square root of 106 to get your answer, c = 10.295.