A cubical Gaussian surface has a side length of $a = 10\, \text{cm}$. Electric field lines are parallel to the $x$-axis as shown. The magnitudes of electric fields through surfaces $ABCD$ and $EFGH$ are $6\, k\, \text{N/C}$ and $9\, k\, \text{N/C}$ respectively. Then, the total charge enclosed by the cube is [Take $\varepsilon_0 = 9 \times 10^{-12}\, \text{F/m}$].