The distance between charges + q and - q is 2 l and between + 2 q and - 2 q is 4 l . The electrostatic…

The distance between charges $+q$ and $-q$ is $2l$ and between $+2q$ and $-2q$ is $4l$. The electrostatic potential at point $P$ at a distance $r$ from centre $O$ is $-\alpha \left[\frac{ql}{r^2}\right]\times {10}^9 \mathrm{V}$, where the value of $\alpha$ is ______. (Use $\frac{1}{4\pi {\epsilon }_0}=9\times {10}^9 \mathrm{N} {\mathrm{m}}^2 {\mathrm{C}}^{-2}$)