Answer:
12
Step-by-step explanation:
If you use the pathagrem therom a^2+b^2=c^2 and fill it in it would be 9^2+b=15^2.
Then just do basic math to simplify the equation
9*9=81
15*15=225
81+b= 225
b= 225-81
b= 144
finally square root 144 and thats how you get 12
