The Attempt at a Solution
we know the electric field at A is 0, so the force is 0.
V = work / charge = U / q = F⋅D / q
the electric field at B is 4 times 3.6N/C = 14.4 N/C
since E = F/q, F = Eq
force, F = 14.4q at point b
V = 14.4q⋅d/q
the q's cancel, d is the distance from A to b which is 4.47
V = 14.4 ⋅ 4.47 = 64.39
is this correct?