Answer: 17.6
Step-by-step explanation: Since you don't know one of the sides, you have to do the pythagorean theorem, which is a^2 + b^2 = c^2 so
210.25 + 100 = 310.25 so then you do the square root of 310.25, which is 17.6 when you round to the nearest tenth, so x = 17.6