Gibbs Energy Questions

The Gibbs energy for the decomposition of ${\text{Al}}_2{\text{O}}_3$ at $500^{\circ }\text{C}$ is as follows:
$$\frac{2}{3}{\text{Al}}_2{\text{O}}_3\to \frac{4}{3}\text{Al}+{\text{O}}_2;{\Delta }_{r}G=+960{\text{kJ mol}}^{-1}$$
The potential difference needed for the electrolytic reduction of aluminium oxide (${\text{Al}}_2{\text{O}}_3$) at $500^{\circ }\text{C}$ is at least:

Using the Gibbs energy change, $\Delta G^{\circ }=+63.3\text{kJ}$, for the reaction:
$${\text{Ag}}_2{\text{CO}}_3(s)\rightleftharpoons 2{\text{Ag}}^{+}(aq)+{\text{CO}}_3^{2-}(aq)$$
The $K_{sp}$ of ${\text{Ag}}_2{\text{CO}}_3(s)$ in water at $25^{\circ }\text{C}$ is: ($R=8.314{\text{J K}}^{-1}{\text{mol}}^{-1}$)