The enthalpy of formation of CO(g), CO2(g), N2O(g), and N2O4(g) is -110, -394, +81, and 10 kJ/mol respectively. For the reaction, N2O4(g) + 3CO(g) → N2O(g) + 3CO2(g), ΔHr (kJ/mol) is?

N2O4(g)+3CO(g)→N2O(g)+3CO2(g)
ΔHreaction=∑Heat of formation of products−∑Heat of formation of reactants
ΔHreaction=[ΔHfN2O+3×ΔHfCO2]−[ΔHfN2O4+3×ΔHfCO]
ΔHr=[+81+3(−394)]−[10+3(−110)]=[81−1182]−[10−330]=[−1101]−[−320]=−1101+320=−781 kJ/mol