Please give explanation

Two points in space, A and B, have electric potentials of +20 V and -50 V, respectively. A sodium ion, Nat, is moved at constant speed from point A to point B. What is the change in the sodium ion's potential energy when going from A -> B? .-4.8 x 10-18 J 4.8 x 10-18 J O-11.0 x 10-18 J 11.0 x 10-18 J