79. A steam turbine with 85% stage efficiency receives steam at 7 MPa and 550°C and exhausts

at 20 kPa. Determine the turbine work.

@ 7 MPa and 550°C: h1 = 3530.9 kJ/kg s1 = 6.9486 kJ/kg-K

@ 20 kPa (0.020 MPa): sf = 0.8320 kJ/kg-K hf = 251.40 kJ/kg

sfg = 7.0766 kJ/kg-K hfg = 2358.3 kJ/kg

A. 1,117 kJ/kg B. 1,132 kJ/kg

C. 1,123.34 kJ/kg D. 1,054.95 kJ/kg