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