Question is attached in the image (ALTS-1 Q28)

Dear student,

According to the Gauss law, the flux passing through any closed surface is equal to the total charge enclosed inside the surface divided by the permittivity of free space.

We just have to find out the total charge enclosed inside this cubical surface. The charges that are present inside this closed surface are-

1. Half the charge of the disk=+3C
2. 3/4th the charge of the rod=+6C
3. Charge placed at (a/4,-a/4,0)=-7C
Hence total enclosed charge=+2C

Hence flux passing through the cube=