Answer:
12
Step-by-step explanation:
Let's call the width x and the length x + 3. Using the Pythagorean Theorem we can write:
(x + 3)² + x² = 15²
x² + 6x + 9 + x² = 225
2x² + 6x - 216 = 0
2(x² + 3x - 108) = 0
2(x + 12)(x - 9) = 0
x + 12 = 0 or x - 9 = 0
x = -12 or x = 9
x cannot be -12 because length/width can't be negative so x = 9 which means that the length is 9 + 3 = 12.
