Given:
(A) $2 \mathrm{CO}(\mathrm{g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow 2 \mathrm{CO}_2(\mathrm{~g})$ in $\quad \Delta \mathrm{H}_1^{\ominus}=-\mathrm{x} \mathrm{kJ} \mathrm{mol}^{-1}$
(B) C (graphite) $+\mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}_2(\mathrm{~g})$; $\Delta \mathrm{H}_2^{\ominus}=-\mathrm{y} \mathrm{kJ} \mathrm{mol}^{-1}$
The $\Delta \mathrm{H}^{\ominus}$ for the reaction
$\mathrm{C}($ graphite $)+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}(\mathrm{g})$ is
