A charge of -2.68 ✕ 10-9 C is at the origin of a coordinate system, and a charge of 7.77 ✕ 10-9 C is on the x-axis at 2.00 m. At what two locations on the x-axis is the electric potential zero? (Hint: One location is between the charges, and the other is to the left of the y-axis.)