For this question, the enthalpy combustion of graphite(carbon) and the enthalpy combustion of hydrogen should be negative right? Because they are exothermic reactions?
I was unable to copy paste the question so I have attached it as a file.
Please kindly let me know.
Thank you,
Lakshmi
PS question is here
Calculate the enthalpy of combustion of methane, given that the enthalpy of formation of methane is -74.6 kJ/mol and the enthalpy combustion of graphite and hydrogen are 393.4 kJ and 285.7 kJ/mol respectively.

yes you are right that they are negative enthalpies because their combustions are exothermic.
Enthalpy Combustion of graphite is a actually enthalpy of formation of CO2
Enthalpy Combustion of hydrogen is a actually enthalpy of formation of H2O
Reaction of combustion of methane is
CH4 +O2 ----> CO2 + 2H2O
(g)      (g)         (g)       (g)

Now use formation enthalpies of the reactants and products  to get enthalpy of above reaction.