Answer:
12
Step-by-step explanation:
Pythogorean Theorem:
a squared + b squared = c squared
9 squared or 81 + ? squared = 15 squared or 225
Inverse Pythagorean Theorem:
c squared - a squared = b squared
225 - 81 = 144
sqrt (144) = 12
12 = b
Hope this helps! Good luck!