Question

a positive point charge q sits at the center of a hollow spherical shell. The shell, with radius R and negligible thickness, has net charge -2q. find an expression for the for the electric field strength (a) inside the sphere, r<R (b) outside the sphere, r>R. in what direction does the electric field point in each case.

Answer 1

Have you tried using Gauss' law?

It is well suited to problems like this.

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/elesph.html