The U.S. government recently released an RFP to construct a second-story fl oor on an existing building at the Pentagon Complex. Separate contractors proposed two methods. Method 1 will use lightweight expanded shale on a metal deck with open web joists and steel beams. For this method, the costs will be $14,100 for concrete, $6000 for metal decking, $4300 for joists, and $2600 for beams. Method 2 will construct a reinforced concrete slab costing $5200 for concrete, $1400 for rebar, $2600 for equipment rental, and $1200 for expendable supplies. Special additives will be included in the lightweight concrete that will improve the heat-transfer properties of the fl oor. If the energy costs for method 1 will be $600 per year lower than for method 2, which one is more attractive? Use an interest rate of 7% per year, a 20 -year study period, and the B/C method.