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