3.7 kg of a fuel is completely burnt to give off 1.665 × 108 joules of energy.…

Calorific value of a fuel is the amount of heat energy released when a unit mass of the fuel is completely burnt. It is defined as Calorific value = Total heat energy released ÷ Mass of fuel burnt, and by convention in school-level science it is expressed in kilojoules per kilogram (kJ/kg).

1. Total heat energy released, given in the question, is 1.665 × 108 J.

2. Mass of fuel burnt is 3.7 kg.

3. Calorific value = 1.665 × 108 J ÷ 3.7 kg = 4.5 × 107 J/kg.

4. Convert joules to kilojoules by dividing by 1000: 4.5 × 107 J/kg ÷ 1000 = 45,000 kJ/kg.

Cross-check: multiplying the value obtained in the previous step by the mass (3.7 kg) reproduces 1.665 × 108 J exactly — the same energy given in the question — confirming the calculation.