As seen from the circuit, between P and Q there is a combination of three capacitors. In this combination two \\\\(4\\ \\mu F\\\\) capacitors are connected in series and this series connection is connected in parallel to the \\\\(2\\ \\mu F\\\\) capacitor.So, effective capacitance of the series combination:\\\\(\\dfrac{1}{C_{eff}}=\\dfrac{1}{C_{1}}+\\dfrac{1}{C_{2}}\\\\)or, \\\\(\\dfrac{1}{C_{eff}}=\\dfrac{1}{4}+\\dfrac{1}{4}\\\\)or, \\\\(C_{eff}=2\\mu F\\\\)Now, this \\\\(2\\ \\mu F\\\\) capacitance comes in parallel with the \\\\(2\\ \\mu F\\\\) capacitance.So, effective capacitance of this parallel combination:\\\\(C'_{eff}=C_{1}+C_{2}\\\\)or, \\\\(C'_{eff}=2\\ \\mu F+2\\ \\mu F\\\\)or, \\\\(C'_{eff}=4\\ \\mu F\\\\)