Answer
$C=9.14$ nF
Work Step by Step
As the total energy is given as
$U=\frac{Q^2}{2C}$
This can be rearranged as:
$C=\frac{Q^2}{2U}$
We then plug in the known values to obtain:
$C=\frac{(1.60\times 10^{-6})^2}{2(140\times 10^{-6})}=9.14\times 10^{-9}=9.14nF$
