But you can figure it out. Look at the formula for ##E##. If you plug in different values for ##r##, you don't get the same number, i.e., the magnitude changes with distance, so the field of a point charge isn't uniform. That means the formulas that apply to a point charge probably aren't useful for this problem.
I'm guessing you feel a bit overwhelmed by the many formulas for the electric field, potential energy, electric potential that you've encountered recently. It might be a good idea to write them all down on a piece of paper and note when each formula is applicable. I suggest this for two reasons: (1) when you do this, you'll probably see there aren't as many formulas as you thought there were, so the topic will seem more manageable; and (2) it's helpful to have this sheet when you're working on homework.
In this problem, you're looking for a relationship between ##\Delta V## and ##E## when ##\vec E## is uniform. Try checking the chapter summary for such a relationship.