Air is expanded by an adiabatic gas turbine from 450 psia and 900°F to 75 psia and 200°F. If the volume flow rate at the exit is 65 ft3/s, the inlet area is 0.75 ft2, and the outlet area is 1.5 ft2; determine the power produced by this turbine in kW. Assume that air is ideal but use both variable and constant specific heats to answer this question and compare your results. Which method should be more accurate?