Please answer attached question, also please give it's explanation.

Observe that the three vertices adjacent to one of connection points of your grid always have the same potential, due to symmetry. Since they do, you can fuse them all together into one. The same goes for the other three vertices adjacent to the other connection point.

Now you have reduced your problem to a simple configuration: (C || C || C) + (C || C || C || C || C || C) + (C || C || C) = 3C + 6C + 3C = 6/5 C

Here + means serial connection and || means parallel connection.