A turbine produces 6245 hp. At the entrance to the turbine, the internal energy of the working substance is 1500 BTU/lbm, elevation is 30 ft, pressure is 1000 psia, density is 1.50 lbm/ft3, and the velocity is 300 ft/sec. At the exit of the turbine the internal energy is 1000 BTU/lbm, elevation is 20 ft, pressure is 5 psia, density is 0.025 lbm/ft3, and the velocity is 100 ft/sec. If 2 BTU/lbm of heat is lost to the environment through the turbine casing, determine the required mass flow rate of the working substance (lbm/hr).