Solving Gauss's Law Problem: Excess Electrons in Plastic Sphere

[A.J.710]

Homework Statement

How many excess electrons must be distributed uniformly within the volume of an isolated plastic sphere 23.0cm in diameter to produce an electric field of 1250N/C just outside the surface of the sphere?

Homework Equations

E=Q/4*pi*ε*r^2

The Attempt at a Solution

I've attempted to find the charge using that equation and got 7.353*10^-9. Then to find the number of electrons I did 7.353*10^-9/1.602*10^-19 and I get 45904610632 electrons. It keeps saying I am wrong and I can't figure out why. Can anyone please tell me if I am doing something wrong.

Thanks

 

[A.J.710]

NEVERMIND. They threw in 23cm as the diameter and not the radius...