Please solve third part of the question for me or give its concept......

) 6.7 A thermal power plant generating 1000 MW of electrical power is located by the side of a river. The overall efficiency of the plant is 40%. (a) What is the total thermal power input to the plant? The McGraw-Hill companies 6.48 Thermal Physics (b) At what rate is waste heat discharged from the plant? (c) If the waste heat is delivered to the river, and if a temperature rise of no more than 5°C is permissible, how much water must be available per second? (b) (Ans: (a) 2500MW (b) 1500MW (c) 7.2 x 10 kg s)