Energy Density in a Parallel Plate Capacitor

The plates of a parallel plate capacitor have an area of $90 \mathrm{c}{\mathrm{m}}^2$ each and are separated by $2 \mathrm{m}\mathrm{m}$. The capacitor is charged by connecting it to a $400 \mathrm{V}$ supply. Then the energy density of the energy stored (in $\mathrm{J} {\mathrm{m}}^{-3}$) in the capacitor is (take ${\epsilon }_0=8.8\times {10}^{-12} \mathrm{F} {\mathrm{m}}^{-1})$