A dielectric slab with $500$ mm $\times 500$ mm cross-section is $0.4\:m$ long. The slab is subjected to a uniform electric field of $\textbf{E}=6 \textbf{a}_x+8 \textbf{a}_y\: KV/mm$. The relative permittivity of the dielectric material is equal to $2$. The value of constant $\varepsilon _0$  is $8.85\times 10^{-12} F/M$ . The energy stored in the dielectric in Joules is
1. $8.85 \times10^{-11}$
2. $8.85 \times 10^{-15}$
3. $88.5$
4. $885$