Equivalent circuit of Question is shown in above figure.
Since C1 = C2 - C3 - C5 - 4μF
So Point a 'and b at same potential. It means there is no charge on C2. Hence C1 and C5 is in series. So effective capacitance will be
Thus, C4 and C5. is in series, So
Now C'and C" is in parallel combination as shown in figure C.
∴ Equivalent capacitance will be-