Electric field of a coaxial conducting rod and shell

[22steve]

Homework Statement

The figure below is a section of a conducting rod of radius R1 = 1.30 mm and length L = 11.00 m inside a thick-walled coaxial conducting cylindrical shell of radius R2 = 10.0R1 and the (same) length L. The net charge on the rod is Q1 = +1.50 10-12C that on the shell is Q2 = −2.00Q1.
Question: What is the magnitude E of the electric field at a radial distance of r = 1.50R2? and
What is the magnitude E of the electric field at a radial distance of r = 4.50R1

Homework Equations

Electric Field = k(Q/(r (sq rt (r^2 + (L/2)^2)))
(I believe that's the only relevant equation)

The Attempt at a Solution

8.99^9 (1.5e-12/(.000585 x sqrt(.000585^2 + (.0013/2)^2)) = 26359

 

[rl.bhat]

Use Gauss' theorem to find the electric field.

 

[22steve]

but all I know is the charge, how can I go from flux to electric field?

 

[rl.bhat]

Flux per unit area is the electric field.