Answer
$U=6.9J$
Work Step by Step
We know that:
$U=2\times \frac{Kq^2}{r}+\frac{Kq^2}{d}$
We plug in the known values to obtain:
$U=2\times \frac{9\times 10^9\times(2\times 10^{-6})^2}{0.014142}+\frac{9\times 10^9\times(2\times 10^{-6})^2}{0.02}=6.9J$
