a turbofan engine on a test stand in the laboratory operates continuously at a thrust level of 60,000 lb with a thrust specific fuel consumption of 0.5 h1. the fuel reservoir feeding the engine holds 1,000 gal of jet fuel. if the reservoir is full at the beginning of the test, how long can the engine run before the fuel reservoir is empty? note: a gallon of fuel weighs 6.7 lb.