Question

At a steam power plant, steam engines work in pairs, the output of heat from one being the approximate heat input of the second. The operating temperatures of the first are 520°C and 320°C, and of the second 310°C and 170°C. If the heat of combustion of coal is 2.8x107 J/kg, at what rate must coal be burned if the plant is to put out 1494 MW of power? Assume the efficiency of the engines is 65% of the ideal (Carnot) efficiency.