Pythagorean theorem . Appreciate the help with this question . Thank you

Answer:
C
Step-by-step explanation:
(Hypotenuse)²=(side 1)²+ (side 2)²
(15)²=(12)²+ a
225=144 + a
225 - 144 = a
81 = a
Square both sides which will become 9 =a
Therefore c is equal to 9 cm