A nonconducting spherical shell of inner radius a=2.00 cm and outer radius b = 2.40 cm has (withing its thickness) a positive charge density p = A/r, where A is a constant and r is the distance from the center of the shell. In addition, a small ball of charge q=45.0 fC is located at that center. What value should A have if the electric field in the shell (a[tex]\leq[/tex]r[tex]\leq[/tex]b) is to be uniform? I know the answer that A value is 1.79[tex]\times[/tex]10-11. The problem is I don't know how to solve it. I don't even know which equation I should use. I tried to start with E = kq/r2, but what is the value of r. It is not specified where should I calculate. Please help. Thank you.