What is the magnitude and sign of the charge?
I really disliked that class, a lot. But it looks like the two locations are on the same side of the charge, and point B is 0.8 meters farther away. If the field decreases by 45 volts in that 0.8 meters, it ought to be easy to figure out what the voltage is if you go the other way. I don’t remember the right equations, whether the field decreases linearly or by the square of the distance. But if your equation is the right one, then the field decreases 45 volts every 0.8 meters, linearly. So if we work backwards from point A, then the voltage at the origin should be (3.2 meters/0.
