Determine electric field at x=1m

1. The problem statement, all variables and given/known data
A. The electric potential in a certain region is
[tex]V=ax^2+bx+c[/tex]
where [itex]a=13\frac{V}{m^2}[/itex], [itex]b=-14\frac{V}{m}[/itex], and [itex]c=50V[/itex].

Determine the electric field at [itex]x=1m[/itex].
Answer in units of [itex]\frac{V}{m}[/itex].

B. Determine the position where the electric field is zero. Answer in units of m.

2. Relevant equations
[itex]∫Edx=V[/itex]

3. The attempt at a solution
Well V=49. I have no doubt about that. So if V is 49 at x=1, wouldn't the electric field also be 49 at x=1?

 

[itex]E=\frac{V}{r}[/itex]. [itex]\frac{49}{1}=49[/itex]. What am I doing wrong?

 

Oh wow. So [itex]V=k\frac{Q}{r}[/itex] isn't correct?

 

Perfect, thank you guys