It has been proposed to use the thermal gradient of the ocean to drive a heat engine. Suppose that at a certain location the water temperature is 22oC at the ocean surface and 4oC at the ocean floor. a) What is the maximum posssible efficiency of an engine operating between these two temperatures? b) If the engine is to produce 1GW of power, what minimum volume of water must be processed (to suck out the heat) in every second? I got 6.1% for a and it's correct, but b) is 900m^3 and I just can't figure it out. I know hot water will decrease by 9 degrees and the cold will increase by 9 degrees, but beyond that I don't know how to proceed.