Total interior and exterior charge of a hollow sphere?

[KoontzyN]

Homework Statement

A hollow conducting sphere has inner radius R and outer radius 1.5R. A +40nC point charge is placed at the center. What is the total charge on the interior and exterior walls of the sphere?

R=10cm

Homework Equations

Gauss's Law
σ = Q_enc/A

The Attempt at a Solution

I'm not too sure where to start. I know Gauss's Law for a sphere is E=Q_enc/4πε₀r² , but I don't know where to go from here.

I also know that to find the charge density σ = Q_enc/A. Plugging in the knowns I get σ= 3.18*10^-7 C/m^2. I'm not sure if that relates to the problem at all. Any help is appreciated.

 

[haruspex]

You are not asked for charge density.

How does the charge on the outer surface compare with that on the inner surface?
Consider the field outside the sphere. How is that affected by the charges on the sphere?