Answer:
x = 25.
Step-by-step explanation:
Since the longer side of the smallest triangle bisects the largest triangle's right angle, all three triangles shown are similar.
As seen in the diagram, the smaller triangle's hypotenuse (15) corresponds to the the largest triangle's hypotenuse (x), and the smaller triangle's shorter side length (9) corresponds to the largest triangle's shorter side length (15). So, we can set up a proportion...
9 * x = 15 * 15
9x = 225
x = 225/9
x = 25
Hope this helps!