Hess Law help Watch
Use Hess's Law to work out the enthalpy of combustion via the enthalpies of formation for the reactants and products.
Hopefully when you did the Hess's triangle for hydrogen you noticed a relationship;
A relationship between the enthalpy of combustion and the enthalpy of formation of water.
Why is that relationship there? Because hydrogen (and the oxygen required in combustion) are elements, so their enthalpy of formation is zero.