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

Considering two dipoles with charges $2q \text{ and } q$, we can write the equivalent setup as shown below:

Therefore, net dipole moment is ${P}_{net} = 6ql$ in the leftward direction.

Potential required, 

$V = \dfrac{K\overset{\to}{p} \cdot \overset{\to}{r}}{{r}^{3}} = \dfrac{9 \times {10}^{9}\left(6ql\right)}{{r}^{2}}\cos \left({120}^{o}\right)$

$= - \left(27\right)\left(\dfrac{ql}{{r}^{2}}\right) \times {10}^{9}$

Therefore, $\alpha = 27$.