Point charge $1$ is placed at a distance $20$ from point charge $2=+3(1=$

$106).$ If we place any point charge $3$ at point $,$ in between these two charges, at a

distance $5$ from $1($as shown in the figure$),$ it will experience no net electric force

$$

$($

$=0).$ Determine: $(5$ points$)$

a$)$ The charge $($magnitude and sign $+/)$ of $1.$

b$)$ The electric potential $()$ due to charges $1$ and $2$ at point $.$