A nuclear power plant generates 750 MW; the reactor temperature is 315oC and a river with water

Question:

A nuclear power plant generates 750 MW; the reactor temperature is 315oC and a river with water temperature of 20oC is available?
(a) What is the maximum possible thermal efficiency of the plant, and what is the minimum rate at which heat must be discarded to the river?
b) If the actual thermal efficiency of the plant is 60% of the maximum, at what rate must beat be discarded to the river, and what is the temperature rise of the river if it has a flow rate of 165 nr3 s-1?