Answer:
x + 12 ft
Step-by-step explanation:
Area = base times height. Here we know the area (x^2 + 9x - 36) and the width (x - 3). Since area = length times width, divide the given area by x - 3.
x^2 + 9x - 36 factors into (x - 3)(x + 12).
Dividing this result by x - 3 yields the length: x + 12 ft
