A paper mill has two steam generators, one at 4.5 MPa, 300?C and one at 800 MPa, 500?C. Each generator feeds a turbine, both of which have an exhaust pressure of 1.2 MPa and isentropic efficiency of 87%, such that their combined power output is 20 MW. The two exhaust flows are mixed adiabatically to produce saturated vapor at 1.2 MPa.what is second-law efficiency for the combined system?