[Potironette]

But then if I know the mass and the force, I can find the acceleration...right?

------------If I can't then you can ignore this bottom part because then that's probably what I did wrong------------
The original problem I had was: "An electron is released from rest in a uniform electric field of strength 400. N/C that points east. Neglecting friction and gravity, calculate the speed of the electron at a point exactly 1.00 mm due west of ts starting point, given that the mass of an electron is 9.11 x 10^-31 kg."

These were the two solutions I had. The first one I did was the top one, then found it was incorrect by checking it with the solution's sheet. The second one is more or less how the teacher showed on the solution sheet to do it.

Err, these are sort of blurry so if it's illegible I can type it out. It's question #2 (imgur wasn't letting me crop the first picture properly for some reason)