First use Pythagorean theorem to find the missing length of the triangle with 10 and 6. So 10^2 - 6^2 will give you an answer. The square root that answer and use that answer along with the length of 15 to find x. It’ll be 15^2 + the previous result^2 = x^2. Square root whatever you get for x^2 and that’s your answer.
