A gas refrigeration cycle with a pressure ratio of 5 uses hellum as temperature of the helium is -6ºC at the compressor inlet and 50ºC at the turbine inlet. Assuming isentropic efficiencies of 90 percent for both the turbine and the compressor, determine (a) the minimum temperature in the cycle, (b) the coefficient of performance, and (c) the mass flow rate of the helium for a refrigeration rate of 25 kW.