According to Gauss’s law, we have Flux = ε0​Charge enclosed​ The enclosed charges are half of the charges in the disc, point charge at (a/4, -a/4, 0), and charge in the rod from point a/4 to a/2, that is, 8 C/4. Therefore, Flux = ε0​3C−7C+48C​​ = ε0​−2C​