Enthalpy of sublimation of iodine is $24 \mathrm{cal} \mathrm{g}^{-1}$ at $200^{\circ} \mathrm{C}$. If specific heat of $\mathrm{I}_2(\mathrm{~s})$ and $\mathrm{I}_2(\mathrm{vap})$ are 0.055 and $0.031 \mathrm{cal} \mathrm{g}^{-1} \mathrm{~K}^{-1}$ respectively, then enthalpy of sublimation of iodine at $250^{\circ} \mathrm{C}$ in $\mathrm{cal} \mathrm{g}^{-1}$ is :