Thermochemistry help!!?

Question

Calculate the standard enthalpy of formation of nitroglycerine using the following thermochemical equation... (subscript will be denoted by brackets)... all reactants are liquid, all products are gasses.
4C(3)H(5)O(9)N(3) => 12CO(2) + 6N(2) + O(2) +6725 kilojoule

Answer 1

1. work out 12 x the enthalpy of formation of CO2. Make sure you keep the negative sign.
2. add 6725 to this value.