Electric potential at the centre of a charged hollow metal sphere is

For hollow or conducting sphere potential at the center is equal to the potential at the surface and 

$$\begin{gathered} \mathrm{V}=\frac{\mathrm{q}}{4{\mathrm{\pi \epsilon }}_0\mathrm{R}} \\ \mathrm{where} \mathrm{R} \mathrm{is} \mathrm{the} \mathrm{radius} \mathrm{of} \mathrm{the} \mathrm{sphere} \end{gathered}$$