A thin spherical conducting shell of radius $R$ has a charge $q$. Another charge $Q$ is placed at the centre of the shell. The electrostatic potential at a point $P$ at a distance $R/2$ from the centre of the shell is :

Question

( A ) $\frac{(q+Q)}{4 \pi \varepsilon_0} \frac{2}{R}$
( B ) $\frac{2Q}{4 \pi \varepsilon_0R} - \frac{2q}{4 \pi \varepsilon_0 R}$
( C ) $\frac{2Q}{4 \pi \varepsilon_0R} + \frac{q}{4 \pi \varepsilon_0 R}$
( D ) $\frac{2Q}{4 \pi \varepsilon_0 R}$