Magnitude of Electric Field: Distance of Proton?

Question

At what distance from a proton is the magnitude of its electric field equal to 3.0 x 10^ N/C? show work.

Answer 1

r = sqrt(kq/E), where k = 8.98755E9 N-m^2/C^2 and q for 1 proton = 1.602177E-19 C. (Explanation is in the ref. page.)

Ans. = 2.190863E-8 m.

Answer 2

For this, use the formula E = kq / r², where k is 9.0 x 10^9 Nm²/C². Rearrange the formula into r = (kq / E)^(1/2) to solve for the distance.

I'd solve it for you, but the power is missing.

By that, I mean 3.0 x 10^? N/C

EDIT: Ok, the power is 6, now let's solve this.

r = (((9.0 x 10^9 Nm²/C²) x (1.6 x 10^-19 C)) / (3.0 x 10^6 N/C))^(1/2)

= (4.8 x 10^-16 m²)^(1/2)

= 2.2 x 10^-8 m