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 8C is placed on the x-axis from $x=a/4$  to  $x=5a/4$. Two point charges 7C and 3C are placed at $(a/4,-a/4,0)$  and  $(-3a/4,3a/4,0),$ respectively. Consider a cubical surface formed by six surface  $x=\pm a/2,y=\pm a/2,z=\pm a/2.$ the charge enclosed in the cubical surface in coulombs is