From the figure $ 1.5\mu F $ and $ 1.5\mu F $ are in parallel. Hence, equivalent capacitance is $ {{C}_{p}}=1.5+1.5=3\mu F $ Again these condensers are connected in series. So, $ \frac{1}{{{C}_{s}}}=\frac{1}{3}+\frac{1}{3}+\frac{1}{3}=1, $ So, $ {{C}_{s}}=1\mu F $