Henry is using a total of 40 ft. of lumber to make a bookcase. The left and right sides of the bookcase are each 8 ft. high. The top, bottom, and two shelves are all the same length, labeled . Part A: Construct an equation to model the situation. (5 points)

Part B: Solve the equation. Show all your steps.
(5 points)

Part C: Use the solution to answer the question in a complete sentence. (5 points)