## standard enthalpies of formation

Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The /_\$\displaystyle H_f$ for $\displaystyle H_2O$ is -291.8 kJ/mol).
/_\$\displaystyle H_f$ = ___ kJ/mol
Im not sure how to solve this problem, can someone help with this?