Answer: Length is 15 ft.
Explanation:
Area of a rectangle is length times width. The problem gives you the area and width. If you put that into the equation (A = wl), you get 135 = 9l. Divide 9 from both sides. You get 15 = l. So l = 15 ft.
Your solved variable is 15. And your original equation was A = w*l. The completed (which is already solved) equation can be written as 135 ft^2 = 9ft x 15ft.