Given that the standard potentials (E°) of Cu^2+ / Cu and Cu^+ / Cu are 0.34 V and 0.522 V respectively, the E^° of Cu^2+ / Cu^+ is:

Given that the standard potentials (E°) of $\displaystyle \mathrm{Cu}^{2+} / \mathrm{Cu}$ and $\displaystyle \mathrm{Cu}^{+} / \mathrm{Cu}$ are $\displaystyle 0.34$ V and $\displaystyle 0.522$ V respectively, the $\displaystyle \mathrm{E}^{\circ}$ of $\displaystyle \mathrm{Cu}^{2+} / \mathrm{Cu}^{+}$ is :