capacitors 5microfarad and 7microfarad are parallel to each other, hence effective capacitance = 5 + 7 = 12microfarad 12microfarad and 6 microfarad are in series then effective capacitance = \(\frac{1}{6} + \frac{1}{12}\) = \(\frac{3}{12}\) then effective capacitance = \(\frac{12}{3}\) = 4microfarad