A fuel gas which is having 95% methane and the balance ethane is burned totally with the 25% excess air. The stack gas leaves the furnace at 900 degrees C and is cooled to 450 degrees C in a waste heat boiler, a heat exchanger in which heat lost by cooling gases is used to produce steam from liquid water for heating. Determine the amount of heat (kJ) that must be transferred from the gas in the waste heat boiler to accomplish the indicated cooling by taking a basis of 100 mol fuel gas fed to furnace.