The calorific value of fuel is the amount of heat produced by the complete combustion of 1 kg of fuel.
Now,
Heat produced by 4.5 kg of fuel = 180000 kJ Therefore, heat produced by 1Kg of fuel = 180000/4.5 = 1KJ/Kg
= 40,000 kJ/kg
Hence, the calorific value of the fuel is 40,000 kJ/kg.