A nonconducting spherical shell, with an inner radius of 4 cm and an outer radius of 6 cm, has charge spread nonuniformly through its volume between its inner and outer surfaces. The volume charge density ? is the charge per unit volume, with the unit coulomb per cubic meter. For this shell ? = b/r where r is the distance in meters from the center of the shell and b = 3 ? C/m2. What is the net charge in the shell?