a
Potential outside the shell, \(V_{outside}\) \(=\frac{\mathrm{KQ}}{\mathrm{r}}\)

where \(\mathrm{r}\) is distance of point from the centre of shel Potential inside the shell, \(V_{\text {inside }}=\frac{K Q}{R}\) 

where \('R"\) is radius of the shell

\(\mathrm{V}_{\mathrm{B}}=\frac{\mathrm{Kq}_{\mathrm{A}}}{\mathrm{r}_{\mathrm{b}}}+\frac{\mathrm{Kq}_{\mathrm{B}}}{\mathrm{r}_{\mathrm{b}}}+\frac{\mathrm{Kq}_{\mathrm{C}}}{\mathrm{r}_{\mathrm{c}}}\)

\(\mathrm{V}_{\mathrm{B}}=\frac{1}{4 \pi \epsilon_{0}}\left[\frac{\sigma 4 \pi \mathrm{a}^{2}}{\mathrm{b}}-\frac{\sigma 4 \pi \mathrm{b}^{2}}{\mathrm{b}}+\frac{\sigma 4 \pi \mathrm{c}^{2}}{\mathrm{c}}\right]\)

\(V_{B}=\frac{\sigma}{\epsilon_{0}}\left[\frac{a^{2}-b^{2}}{b}+c\right]\)