The mass fractions of a mixture of gases are 15 percent nitrogen, 5 percent helium, 60 percent

Question:

The mass fractions of a mixture of gases are 15 percent nitrogen, 5 percent helium, 60 percent methane; and 20 percent ethane. This mixture is expanded from 200 psia and 400oF to 15 psia in an adiabatic, steady-flow turbine of 85 percent isentropic efficiency. Calculate the second law efficiency and the exergy destruction during this expansion process. Take T0 = 77oF.

$The mass fractions of a mixture of gases are 15$