1. The problem statement, all variables and given/known data 2. Relevant equations Vab = ∫ E*dr 3. The attempt at a solution For part (b) I am not sure if I should set the upper and lower bound of the integral from "R" to "2R" or "2R" to "3R". If done so, this would give me V2R = Vab * ln|3R/2R| / ln |3| instead of what is on the image.