Answer:
36 units
Step-by-step explanation:
First calculate the length of side a. Using the Pythagorean Theorem, we find that 15^2 = 12^2 + x^2, or 225 - 144 = x^2. Thus, x^2 = 81 and the length of side a is √81, or 9, units.
Then the perimeter is the sum of all three side lengths:
15 + 9 + 12 = 36 units
