The figure is a large right triangle and therefore the pythagorean theorem can be applied. According to the pythagorean theorem, a right triangle can have legs that are three and four units with a five unit hypotenuse.
In this example, one leg is 15 units so the other must be 20 units with a 25 unit hypotenuse. The hypotenuse is equal to x plus 9 so the value of x must be 16.
final answer x=16
