An ideal-gas mixture with 20 kmol of oxygen, 75 kmol of nitrogen and 5 kmol of carbon dioxide enters an adiabatic turbine at 1.4 MPa and 600 K steadily. The mixture is then expanded to a pressure of 100 kPa. If the isentropic efficiency of the turbine is 85%. Determine:

a. The actual work output of the turbine per unit mass of the mixture, in kJ/kg.
b. The specific entropy generation during the expansion process, in kJ/kg. K.