Propane(C_3H_8 Delta H_f = -104.63 kJ/mol) reacts with oxygen to produce carbon dioxide (CO_2 Delta H_f = -393.5 kJ/mol) and water (H_2O DeltaH_f = -241.82 kJ/mol) According to the equation Down below C_3H_8 + 3O_2 -> 3CO_2 + 4H_2O.

Why is the Enthalpy of Combustion of C_3H_8 in the reaction that I showed above?

Any help would be greatly appreciated. (also if you could help show how you did it that would be nice)