A disk of radius a/4 having a uniformly distributed charge 6C is placed in the $x-y$ plane with its centre at $(-a / 2,0,0)$. A rod of length a carrying a uniformly distributed charge 8 C is placed on the x -axis from $\mathrm{x}=\mathrm{a} / 4$ to $\mathrm{x}=5 \mathrm{a} / 4$. Two point charges -7 C and 3 C are placed at $(\mathrm{a} / 4,-\mathrm{a} / 4,0)$ and ( $-3 a / 4,3 a / 4,0$ ), respectively. Consider a cubical surface formed by six surfaces $x= \pm a / 2, y= \pm a / 2, z= \pm a / 2$. The electric flux through this cubical surface is