Total mass of fuel = 4.5 kg
Heat produced by burning the given mass of fuel = 180,000 kJ.
We know that calorific value of fuel
Heat produced in kJ ÷ Total mass burnt
= 180,000 kJ ÷ 4.5 kg = 40,000 kJ/kg
Hence, the calorific value of the given fuel = 40,000 kJ/kg