Electric field at a distance greater than the radius of sphere

[rocapp]

Homework Statement

A solid ball of radius r_b has a uniform charge density ρ.

What is the magnitude of the electric field E(r) at a distance r>r_b from the center of the ball?

Homework Equations

E(r) = (Q/ε)*1/Area

The Attempt at a Solution

If Q=ρr_b

and Area = (4/3)πr³,

then E(r) = $\frac{ρr_b}{ε*(4/3)*πr³}$


However,
the correct answer is in the image attached.
E(r)=

 

[barryj]

Area is not (4/3) pi r^3

Also, Idon't think q = prb

 

[rocapp]

Oh. I get it now. Thanks!