heidleman industries is considering two types of materials for roofing its warehouses. epdm is an elastomeric polymer synthesized from ethylene, propylene, and a small amount of diene monomer, compounded with carbon black processing oils and various cross-linking and stabilizing agents. the 75 mil thickness will cost $5.50 per square foot and will last for 10 years. a thin sheet aluminum (tsa) roof will cost $7.00 per square foot, but it will last for 15 years. using an interest rate of 10% per year, calculate the annual worth per square foot for the epdm and tsa roof and which alternative should be selected.