A 35.0-nC charge is placed at the origin and a 55.0-nC charge is placed on the +

Question:

A 35.0-nC charge is placed at the origin and a 55.0-nC charge is placed on the + x -axis, 2.20 cm from the origin.
(a) What is the electric potential at a point halfway between these two objects?
(b) What is the electric potential at a point on the + x -axis 3.40 cm from the origin?
(c) How much work does it take for an external agent to move a 45.0-nC charge from the point in (b) to the point in (a)?