During the combustion of fuel weighing 100 g, 10 kg of water was heated by 80 degrees.

Data: m (mass of fuel burned) = 100 g (0.1 kg); mw (mass of water heated by fuel combustion) = 10 kg; Δt (set change in water temperature) = 80 ºС.

Constants: C (specific heat capacity of water) = 4200 J / (kg * ºС).

The specific heat of combustion of the fuel is determined from the equality: q * m = C * mw * Δt, whence q = C * mw * Δt / m.

Calculation: q = 4200 * 10 * 80 / 0.1 = 33.6 million J / kg (33.6 MJ / kg).

Answer: The specific heat of combustion of the burnt fuel is 33.6 MJ / kg (natural gas).