Two different fuels are being considered for a 1 MW (net output) heat engine which can operate between the highest temperature produced during the burning of the fuels and an atmospheric temperature of 300 K. Fuel A burns at 2,500 K, delivering 50 MJ/kg (heating value) and costs $2.00/kg. Fuel B burns at 1,500 K, delivering 40 MJ/kg and costs $1.50/kg. Compare the fuel costs per hour of fuel A and fuel B, assuming that the heat engine operates
a. at Carnot efficiency
b. at 50% of Carnot efficiency