Answer
$V=7.19\times 10^{-10}V$
Work Step by Step
We know that
$V=K\frac{q_1}{d_1}+K\frac{q_2}{d_2}$
We plugin the known values to obtain:
$V=9\times 10^9\times \frac{-2\times 1.6\times 10^{-19}}{4}+9\times 10^9\times \frac{2\times 1.6\times 10^{-19}}{2}$
$V=7.19\times 10^{-10}V$