The work done by an external force to move a $-7\mathrm{.}50C$ charge from point A to point B is $25\mathrm{.}0{10}^{-4}J.$ If the charge was started from rest and had $4\mathrm{.}82{10}^{-4}J$ of kinetic energy when it reached point B $,$ what must be the potential difference between A and B $?$