Consider a thick spherical shell with inner radius R; and outer radius Ro, with a total charge +Q distributed uniformly over its volume - but only in the filled volume. There is no charge in the empty hole in the middle (r Ro). Again, be clear about what you are imagining. (Hint: You already should know what this answer should come out to, so that lets you check your answer, but you still must carefully justify your work using Gauss's Law and not just write down the answer based on prior knowledge. )