A charge of +18.0nC is placed on the y-axis at y=-12 cm and a charge of -18.0 nC is placed on the y-axis at y=6.00 cm. a) determine the electrical potential at y=18.0 cm b) What is the difference in potential, ΔV, between this point and the point y=0.00 cm, where ΔV=V18-V0.00?