System of charges in an electric field

A charge, $q_1=4\mu \text{C}$‍, is located at $(0,0,-5\text{m})$‍ in a region with an external electric field.

The potential in the region varies as, $V(\mathbf{r})=\left(120{\displaystyle \frac{\text{V}}{\text{m}}}\right)r$‍, where $r$‍ is the distance from the origin in $\text{m}$‍.

An external agent slowly moves a second charge, $q_2=-1\mu \text{C}$‍, from infinity to $(0,0,5\text{m})$‍.

$\times {10}^{-3}\text{J}$‍