Question

A charge q of 7.3 × 1015 coulomb moves from point A to point B in an electric field. If the potential energy of the charge at point A is 3.5 × 10-12 joules and that at point B is 1.3 × 10-12 joules, what is the potential difference between point A and B?

Answer 1

1.3 × 102 volts

3.0 × 102 volts

3.5 × 103 volts

6.8 × 103 volts

Answer 2

The charge is \[7.3 \times 10^{-15}\] coulombs not \[7.3 \times 10^{+15}\] coulombs.
Potential difference is work done per unit charge and is measured in J/C = V.
So you know the change in potential energy is the work done to move the charge and you know the charge so you can find the potential difference.