Step-by-step explanation:
(a) It is known that relation between charge and volume is as follows.

=

=

=
Now, according to Gauss's law

=

= 3.68

Hence, the electric flux through this cubical surface if its edge length is 4.00 cm is 3.68
.
(b) Similarly, we will calculate the electric flux when edge length is 16.8 cm as follows.

=

=

=
Now, according to Gauss's law

=

= 2.72

Therefore, the electric flux through this cubical surface if its edge length is 4.00 cm is 2.72
.