1. The problem statement, all variables and given/known data A steam-electric power plant delivers 900 MW of electric power. The surplus heat is exhausted into a river with a flow of 5.51×105 kg/s, causing a change in temperature of 1.35 oC. What is the efficiency of the power plant? What is the rate of the thermal source? 2. Relevant equations Q=cm(delta T) c=4.186 J/g*Celsius 3. The attempt at a solution I know how to answer the first question already: Q=(4186 J/kg C)(5.51E5 kg/s)(1.35 C) Q=3113756100 J/s (J/s=Watt) Convert from Watt to Megawatt --> 3113.76 MW 900+3113.76=4013.76=Total output 900/total output=0.2242=22.42 % I don't know how to calculate the rate of the thermal source. What am I missing?