Answer: 15
Explanation: X^2 + 20^2 = 25^2 because of Pythagorean Theorem (a^2 times b^2= c^2). This means that when you have a right triangle, the square of each of small leg of the triangle will add up to the square of the longest leg opposite of the 90 degree angle, more known as the hypotenuse. You can find x squared by subtracting 400 from 625 to get 225. X is the square root of 225, which is 15.