Part A

If the potential $($relative to infinity$)$ due to a point charge is $V$ at a distance $R$ from this charge, the distance at which the potential $($relative to infinity$)$ is $V=4\mathrm{.}00V$ is

$8\mathrm{.}00$ R $.$

$4\mathrm{.}00$ R $.$

$0\mathrm{.}250R.$

$0\mathrm{.}125$ R $.$