The question I am having trouble with shows an image of 2 different conductors, one is at +300 volts, while the other is -600 volts with a few lines going in between which circle around. The points on the equipotential surface are on lines labeled as a (which lies on a -200V line) and the other point is b (lies on -400V line). The question is asking how much work is done by an external agent if the electron is moved from A to B? I have had so much trouble finding an equation to fit the information given. I also have no idea on how to approach this problem.