By superposition, what is meant here is that the cavity given to you can be considered as a sphere of charge density negative of that of the larger sphere. So basically you have to consider a negatively charged sphere superposing with the larger positively charged one only in the region where...
I am a first year Physics undergraduate studying in India at BITS Goa. I plan to take up a career in research if everything goes as desired. I do painting as a hobby and hold deep interest in Rubik's cube and similar puzzles. I look forward to discussing Physics with you people :)