Answer:
15
Step-by-step explanation:
Use A square + B square = C square
it's Pythagorean Theorem
9 squared + 12 squared = 9^2 + 12^2
9^2 + 12^2 = 9*9 + 12*12
9*9 + 12*12 = 81+144
81 + 144 = 225
square root of 225 = 15
there is your answer, 15
