You have to write an expression to represent the area of the rectangle. The width can be w, and the length can be 2w-9. Since the parking lot is a rectangle, you multiply the length by the width to get your area. w(2w-9) is 2w^2-9w=221. The only value of w that satisfies this equation when substituted is 13, so that is your width. 2(13)-9 is 26-9 is 17, so the length is 17.
Explanation: Denominators of a fraction can be equivalently written as their value to the power of negative 1. In this case the denominator expression itself has an exponent of 6, which taken to the power of negative one becomes -6:
