An engineer is analyzing three different devices that can save 10% of the yearly energy consumption for a nuclear power plant. The devices respective costs and useful lives are given in the following table: Description Initial cost, $ Yearly operating cost, $ Maintenance cost every five years, $ Useful life, years Device X 5,500 550 600 10 Device Y 6,100 450 700 15 Device Z 10,500 750 1,200 Infinity Answer the following questions assuming that Devices Y and Z can be replaced with identical replacements at the end of their useful lives and the interest rate is 10%. 5. If present worth analysis (PWA) is performed to determine the best alternative, the analysis period for Device Y should be______? (a) Infinity (b) 15 6. The net present cost (NPC) of Device X is (a) $ 19,966 (b) $ 13,667 7. The net present cost (NPC) of Device Y is (a) $ 19,966 (b) $ 13,667 (c) 10 ? (c) $ 15,433 ? (c) $ 15,433 2 (d) 30 (d) $ 21,677 (d) $ 21,677