Verified answer

Convert 43.0 g into moles of CaCO3, and multiply it by the enthalpy.

43.0 g / 100.0869 g/mol = 0.430 mol

0.430 mol x 178 kJ/mol = 76.5 kJ

The enthalpy gives you how much heat is transferred per mole, so first find the moles and multiply it by the enthalpy.

if the -6278kJ is the warmth of the reaction as written, ie for the combustion of two moles benzene then combustion of two x seventy 8.11g produces 6278kj or 24.3 g produces (6278/(2 x seventy 8.11)) x 24.3 = 976.5 kJ