\[ V = \frac{1}{4\pi\epsilon_0} \frac{Q}{r} = 9 \times 10^9 \, \text{Nm}^2 \, \text{C}^{-2} \times \frac{4 \times 10^{-7} \, \text{C}}{0.09 \, \text{m}} \]

\[ = 4 \times 10^4 \, \text{V} \]

\[ W = qV = 2 \times 10^{-9} \, \text{C} \times 4 \times 10^4 \, \text{V} \]

\[ = 8 \times 10^{-5} \, \text{J} \]

No, work done will be path independent. Any arbitrary infinitesimal path can be resolved into two perpendicular displacements: One along \(\mathbf{r}\) and another perpendicular to \(\mathbf{r}\). The work done corresponding to the later will be zero.