A well-insulated rigid tank contains 6 lbm of saturated liquid-vapor mixture of water at 35 psia. Initially, three-quarters of the mass is in the liquid phase. An electric resistance heater placed in the tank is turned on and kept on until all the liquid in the tank is vaporized. Assuming the surroundings to be at 758F and 14.7 psia, determine (a) the exergy destruction and (b) the second-law efficiency for this process.