What is potential difference uniform electric field

[Blitzp22]

Homework Statement

What is the potential difference (in V) between xi = 18.5 cm and xf = 82.2 cm in the uniform electric field Ex = 4920 V/m?

Homework Equations

Not sure?

The Attempt at a Solution

Its simple but I am having problems figuring it out. I have a feeling it has to do with q1 and q2.

 

[Blitzp22]

Solved. Not as bad as I thought