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

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

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

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