A steam power plant supplies 5500 kg of steam per hour at 10 bar and 95% dryness fraction using the feed water at 41.5°C when using 700 kg of coal per hour having the calorific value 31100 kJ/kg. Determine the efficiency of the boiler which is fitted with the economizer.It is estimated that the feed water can be raised to 93.5°C,other conditions remain unchanged and the efficiency of the boiler increases by 5%.