$17$c

Two charged particles A and $B$ carry a charge of $+2q$ and $-q$ respectively.

$($i$)$ What is the electric potential, $V,$ at a distance $x$ from the origin on the $x-$axis?

$($ii$)$ A third charged particle, $C,$ carrying a charge of $+q$ is placed at the $x=0$ Calculate the potential energy in the system, given that $l=0\mathrm{.}2m$ and $q=12nC.$

$($iii$)$ Determine the work done by the electric force when C is brought from infinity to the origin.