Calculate the work against gravity require to build the structure out of brick. Assume the brick has a density of 80 lb/ft^3. A tower has a height of 20ft and a square base of side 10ft. This is what I tired to do. I may have gotten it right, but the units or something may have been off. I am hoping one of you will be able to help me. Volume of layer = 10 x 10 Δy ft^3 = 100Δy ft^3 Mass of layer = 80 lb/ft^3 x 100Δy ft^3 Force on layer = 9.8 x 80 x 100Δy = 78400 Taking the integral of 78400y from limits 0 to 20 equals 15,680,000, but the answer in my solutions manual says the answer should be 1.6x10^6 ft-lb. Can anyone help me out?