Answer:
x + 3
Step-by-step explanation:
1. The area of a rectangle is length times width.
A = LW
2. Solve for the width by dividing both sides of the equation by the length:
W = A / L
3, Plug in the expressions for A and L:
W = (3x² + 9x) / 3x
W = (3x² / 3x) + (9x / 3x)
W = x + 3