The potential difference (V) between two points in an electric field is given by the work done (W) in transferring a charge (Q) from one point to another, according to the formula:
\( V = \frac{W}{Q} \)

Given that the work done is 30 joules and the charge transferred is 5 millicoulombs (which is 5 x 10^-3 coulombs), we can substitute these values into the formula:

\( V = \frac{30 \, \text{J}}{5 \times 10^{-3} \, \text{C}} = 6 \times 10^{3} \, \text{V} \)

So, the potential difference between points B and A is 6.0 x 10³ V (Option D).