Use the Pythagorean theorem to get the length PQ. Since ∆PQT is a right triangle, we have
PQ² + 15² = 25² ==> PQ = √(25² - 15²) = √400 = 20
Use the theorem again to get the length x :
x ² + 12² = PQ² ==> x = √(20² - 12²) = √256 = 16
