Electric field of coax cable problem

[Punchlinegirl]

A coaxial cable has a charged inner conductor, with charge 8.3 $$\mu C$$ and radius 2.917 mm, and a surrounding oppositely charged conductor, with charge -8.3 $$\mu C$$ and radius 5.997 mm. Assume the region between the conductors is air and neglect end effects. The length of the cable is 60 m. What is the magnitude of the electric field halfway between the two cylindrical conductors. Answer in units of V/m.
I got help with this problem, but it still isn't working out. We used Gauss's Law. To find the radius of the Gaussian surface, we used R-r/2 + r.
So .005997 - .002917 /2 + .002917 = .004457
Then to get the E, you do $$q_e_n_c / E_o *A$$
With the area of a cylinder= $$2\pi r^2 + 2\pi *r*h$$
So [tex] 8.3 x 10^-6 / 8.85 x 10^-12 *(2\pi (.004457)^2 + 2 \pi * (.004457)(60))
Which gave me 5.58 x 10^11, which isn't right.. can someone please help me?

 

[Astronuc]

See if this helps - http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capcyl.html#c2

 

[Punchlinegirl]

Ok so the equation that this page gives for the E-field is
$$E= \lambda / 2\pi * E_o * r$$, but since the charge isn't uniform, I don't think I can use it...