inner radius $=2 R$

outer radius $=3 R$

charge $=+2 Q$ hollow sphere a total charge $=-Q$

The electrostatic potential energy of this system$=$

By indication, inner wall of hollow sphere is induced with share $-2 Q$ and its outer surface with charge.

Two conducting concentric, hollow sphere $A$ and $B$ have radii $a$ and $b$ respectively.

$V=\frac{1}{4 \pi \in_{0}} \times \frac{Q}{R}$

when, it is given that,

$V^{1}=\frac{1}{4 \pi \in_{0}} \frac{2 Q}{2 R}$

$V^{11}=\frac{1}{4 \pi \in_{0}} \frac{Q}{3 R}$

$V=\frac{Q}{4 \pi \in_{0}}\left(\frac{2 Q}{2 R}+\frac{Q}{3 R}\right)$

$=\frac{1}{4 \pi \in_{0}} \frac{6 Q+2 Q}{6 R}$

$=\frac{7 Q^{2}}{24 \pi \in_{0} R}$