The cell potential for the given cell at $298 \mathrm{~K} \mathrm{Pt}\left|\mathrm{H}_2(\mathrm{~g}, 1 \mathrm{bar})\right| \mathrm{H}^{+}(\mathrm{ag}) \| \mathrm{Cu}^{2+}(\mathrm{aq}) \mid \mathrm{Cu}(\mathrm{s})$ is 0.31 V . The pH of the acidic solution is found to be 3 , whereas the concentration of $\mathrm{Cu}^{2+}$ is $10^{-x} \mathrm{M}$.
The value of $x$ is $\_\_\_\_$ .
(Given: $\mathrm{E}_{\mathrm{Cu}^{2+} / \mathrm{Ou}}^{\ominus}=0.34 \mathrm{~V}$ and $\frac{2.303 \mathrm{RT}}{\mathrm{F}}=0.06 \mathrm{~V}$