We know that ΔBAC and ΔBED are similar becuase of the AA Postulate (they both have a right angle and they both share ∠B). Since AC is 15/3 = 5 times longer than ED, the scale factor is 5 which means AB is 5 times longer than EB. This makes EB = 25 / 5 = 5. Since AB = AE + EB and we know that AB = 25, AE = x and EB = 5, 25 = x + 5 which means x = 20.
