The distance between charges +q and -q is 2 l and between +2 q and -2 q is 4 l. The electrostatic potential at point P at a distance r from center O…

The distance between charges $\displaystyle +q$ and $\displaystyle -q$ is $\displaystyle 2 l$ and between $\displaystyle +2 q$ and $\displaystyle -2 q$ is $\displaystyle 4 l$. The electrostatic potential at point $\displaystyle P$ at a distance $\displaystyle r$ from center $\displaystyle O$ is $\displaystyle -\alpha\left[\frac{q l}{r^2}\right] \times 10^9 V$, where the value of $\displaystyle \alpha$ is $\displaystyle \_\_\_\_$. (Use $\displaystyle \frac{1}{4 \pi \varepsilon_0}=9 \times 10^9 N m^2 C^{-2}$ )