Thermodynamics

Given, $\Delta G^{\circ}=-502 \mathrm{~kJ} \mathrm{~mol}^{-1}$ for the dissociation of ,

$\mathrm{Mg}(\mathrm{OH})_2(s) \rightleftharpoons \mathrm{Mg}^{2+}(a q)+2 \mathrm{OH}^{-}(a q)$ at 298 K . Find the $K_{\mathrm{sp}}$ value.

$(R=8314 \mathrm{~J} / \mathrm{mol} \cdot \mathrm{K})$