A parallel plate capacitor with width 4 cm, length 8 cm and separation between the plates of 4 mm is connected to a battery of 20 V. A dielectric…

A parallel plate capacitor with width $\displaystyle 4$ cm, length $\displaystyle 8$ cm and separation between the plates of $\displaystyle 4$ mm is connected to a battery of $\displaystyle 20$ V. A dielectric slab of dielectric constant $\displaystyle 5$ having length $\displaystyle 1$ cm, width $\displaystyle 4$ cm and thickness $\displaystyle 4$ mm is inserted between the plates of parallel plate capacitor. The electrostatic energy of this system will be \_\_\_\_ $\displaystyle \epsilon_0 \mathrm{~J}$. (Where $\displaystyle \epsilon_0$ is the permittivity of free space)