IIT JEE Advanced 2009 Paper 1

A disk of radius a/4 having a uniformly distributed charge 6 C is placed in the xy-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 x = a/4 to x = 5a/4. Two point charges -7 C and 3 C are placed at (a/4, - a/4, 0) and (-3a/4, 3a/4, 0), respectively. Consider a cubical surface formed by six surfaces x = ±a/2, y = ±a/2, z = ±a/2. The electric flux through this cubical surface is