A)Two point charges, +3.90 ìC and -7.50 ìC, are separated by 3.30 m. What is the electric potential midway between them?

B)The drawing shows four point charges. The value of q is 1.3 ìC, and the distance d is 0.95 m. Find the total potential at the location P. Assume that the potential of a point charge is zero at infinity.

For the potential at any point, add up the kQi/Ri terms due to all surrounding charges. Ri is the distance from each charge Qi. k is the Coulomb constant.