this is a screen shot of a past paper exam, sorry that I could not get better quality.
I am struggling to answer this question (b) and (c), I believe that once I solved for (c) it should be easy to get (d)
If this was the other way round(metal ball surrounded by a rubber dielectric) the I could solve it but this way seems tricky.
I would really appreciate it if you could help me out
I believe that for a metal(conductor) to have a Q charge total spread over there must -Q on the underside of metal shell(due to negligible thickness and no other charge, but possibly what the metal shell could be covering), thus there must be an overall Q source charge inside the rubber because the sum of surface bound charge and volume charge should = 0. But this doesn't help my case it seems