13. A turbojet engine operates on the Brayton cycle and has the following parameters: the compressor pressure ratio is 12, the turbine inlet temperature is 1300C, the compressor inlet temperature is 25C, the isentropic efficiency of both the compressor and the turbine is 85%, and the ambient temperature is 15C. Determine the thermal efficiency and specific thrust of the engine if the nozzle exit velocity is 650 m/s and the mass flow rate of air through the engine is 50 kg/s.