Answer
$3.5\ pF$
Work Step by Step
If the charge on each plate changes, the capacitance does not change. because the charge q on the capacitor is proportional to the applied voltage.
$q \propto V$
The proportionality constant is C and is referred to as capacitance of the device
$q = CV$
Substituting the values of $q$ and $V$ and finding $C$:
$C = 3.5\times 10^{-12} F = 3.5\ pF$
