Electric power is to be generated by installing a hydraulic turbine$-$generator at a site $70$ m below the free surface of a large water reservoir that can supply water at the rate of $1500$ kg$/$s steadily. Write the energy equation and using that equation calculate the maximum possible power output in kW$.$ If the power output of the turbine is $800$ kW and the electric power generation is $750$ kW$,$ determine the turbine efficiency and the combined turbine$-$generator efficiency of this plant.