An external agent does +4.0×10−4J of work to move a −2.0μC point charge slowly from point A to point B. The charge is then released from rest at B and accelerates solely under the electric force to point C, where the electric potential equals that at A. When the charge reaches point C, its kinetic energy is 4.0×10−4J. Determine the electric potential at point B relative to point A.