Two things:

1) you're not off by a factor of 2 (which implies a conceptual misunderstanding); the impossible answer (imaginary solution) is supposed to be the correct one, you just made arithmetic errors (namely too much rounding).

2) Well actually I said both things already. The headache is due to your rounding the acceleration and the initial velocity to those values.

Assuming that the acceleration and initial velocity are not given by the problem (because they're what's causing the headache), here's the solution.

The quadratic is supposed to have one solution only, and the positive discriminant comes out of rounding errors (b^2 - 4ac = 6.29 while either of b^2 or 4ac is of 12 orders of magnitude away). When you rounded the acceleration and initial velocity to what you have in the OP, you made the discriminant negative.

@__Marksman Bryan__

Bonus: The field is just a force without a victim, so calculate the electric force on another charge (make up one), if you have to, then divide by the magnitude of the victim charge. Otherwise, E = kq/r^2.

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