Example $3$

A positive test charge of $1\mathrm{.}5{10}^{-6}C$ is placed in an electric field $10$ cm from another charge of magnitude $-5\mathrm{.}0{10}^{-6}C$ that is anchored in place. What is the potential difference between the test charge's initial position and a point $5\mathrm{.}0$ cm closer to the negative charge?

$q_t=1\mathrm{.}5{10}^{-6}C,q_1=-5\mathrm{.}0{10}^{-6}C,r_B=0\mathrm{.}05,r_A=0\mathrm{.}1$