Answer:
ΔV = 78 V
Step-by-step explanation:
The potential at a point due to a point charge is given as:

where,
V = Potential at the point
k = Colomb's Constant = 9 x 10⁹ Nm²/C²
q = charge = 3.25 x 10⁻⁹ C
r = distance
AT POINT A:

AT POINT B:

Now, the potential difference will be:

ΔV = 78 V