Answer
We can put two capacitors in parallel, and then we can put another capacitor in series with these two capacitors.
Work Step by Step
We can find the equivalent capacitance when we put two capacitors in parallel:
$9.0~pF+9.0~pF = 18.0~pF$
We can find the equivalent capacitance when we put another capacitor in series with these two capacitors:
$\frac{1}{C_{eq}} = \frac{1}{18.0~pF}+\frac{1}{9.0~pF}$
$\frac{1}{C_{eq}} = \frac{3}{18.0~pF}$
$C_{eq} = 6.0~pF$
We can put two capacitors in parallel, and then we can put another capacitor in series with these two capacitors.
