How is hess's law used to calculate the enthalpy of a reaction apex?

Hess's Law of Constant Heat Summation states that regardless of the multiple steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. Thus, the enthalpy change is the same whether the reaction takes place in one step or in a series of steps. We can use Hess's Law by adding or subtracting chemical reactions with the same products or reactants. 

Ithink it’s carbon dioxide