A disk of radius a/4 having a uniformly distributed charge 6C is placed in the xy 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 surfaces , . The electric flux through this cubical surface is

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