GATE EC 2016 Set 2 Q52 — Electronic Devices

The parallel-plate capacitor shown in the figure has movable plates. The capacitor is charged so that the energy stored in it is $E$ when the plate separation is $d$. The capacitor is then isolated electrically and the plate are moved such that the plate separation becomes $2d$.

At this new plate separation, what is the energy stored in the capacitor, neglecting fringing effects?