From the enthalpies of reaction

Question

2C(s)+O2(g)�¨2CO(g)ƒ¢H=−221.0kJ
2C(s)+O2(g)+4H2(g)�¨2CH3OH(g)ƒ¢H=−402.4kJ
calculate ĢH for the reaction
CO(g)+2H2(g)�¨CH3OH(g)

Answer 1

Reverse equation 1 and add to equation 2. Divide the final equation by 2.
Add the dH values; when an equation is reversed, change the sign of dH.