Answer
$W=1.8\times 10^{-10}J$
Work Step by Step
We know that:
$W=\Delta U=\frac{q_1q_2}{4\pi \epsilon_{\circ}}(\frac{1}{r}-\frac{1}{\sqrt{r^2+x^2}})$
We plug in the known values to obtain:
$W=(-9\times 10^9)(-6\times 10^{-6})(8.99\times 10^9)(\frac{1}{1.5}-\frac{1}{\sqrt{{(1.5)^2}+(3)2}})=1.8\times 10^{-10}J$
