For the reaction

Fe2​O3​( s)+3CO(g)​→2Fe(s)​+3CO2​( s)
ΔG∘=−31.3 kJ.

Calculate the standard free energy of formation of the ferric oxide, Fe2​O3​, if ΔG∘ of CO=−137 kJ/mol and ΔG∘ f of CO2​=−394 kJ/mol.