Answer:
b = 12
Step-by-step explanation:
a² + b² = c²
a and b are the length of the sides in the right triangle and c is the hypotenuse.
since we know one leg and the hypotenuse, we can find the other leg.
9² + b² = 15²
81 + b² = 225
b² = 225 - 81
b² = 144
b = 12
