A cell is written $\text{Mg}(s) \mid \text{Mg}^{2+}(aq) \parallel \text{Ag}^+(aq) \mid \text{Ag}(s)$. Using $E^\circ$ values of $-2.37\ \text{V}$ and $+0.80\ \text{V}$, what is $\Delta G^\circ$ for each mole of magnesium that dissolves?