A charged paint is spread in a very thin uniform layer over the surface of a pla

Question

A charged paint is spread in a very thin uniform layer over the surface of a plastic sphere of diameter 13.0 cm , giving it a charge of -15.0micro coulombs.
So I've looked at the other questions similar to this however on the last part C) the equations never seems to work.

Part c)
Find the electric field 7.00 cm outside the surface of the paint layer.

So pretty much what I've done is taken the equation
E=q/[4piE_0r^2]

Simplifying I get the constant K=8.988*10^9 which makes the equation look like:

E=K*q/(r^2)

Where r= .065m (Original radius) +.07m=.135m

Plugging that into the equation:
E=[8.988*10^9]*(-15*10^-6)/(.135^2)
E=-7397530.864

Am I plugging in the incorrect numbers or is something wrong with my equation?
Thanks in advance.

Explanation / Answer

If the charge is uniformly distributed on the surface of a sphere, the electric field outside the sphere will be the same as if the entire charge were concentrated in the center of the sphere. The electric field inside the sphere would be zero. Because the electric field in a would be measured inside the (uniformly-charged) sphere, the electric field for part a would be zero. For the other two cases, we get E = q / (4peor²) For outside the paint layer, r = 0.065 m, so the electric field would be -1.50*10^-5 C / (4p(8.85*10^-12 C²/J-m)(0.065 m)²) = -3.194e7 N/C, the negative sign means the electric field is in toward the sphere.

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