Helium at 660 K expands in a turbine to 369 K during which 84 kJ/kg of heat was lost to the surroundings which are at 27 °C. The pressure across the turbine was 6.0, What is the isentropic efficiency...

Helium at 660 K expands in a turbine to 369 K during which 84 kJ/kg of heat was lost to the surroundings which are at 27 oC. The pressure across the turbine was 6.0, What is the isentropic efficiency "%"?

Extracted text: Helium at 660 K expands in a turbine to 369 K during which 84 kJ/kg of heat was lost to the surroundings which are at 27 °C. The pressure across the turbine was 6.0, What is the isentropic efficiency "%"? Select one: A. 76.25% B. 86.17% C. 81.38% D. 78.64% E. 87.25% X