Answer:
Step-by-step explanation:
Part a)
For a position of point inside the inner shell we can use Gauss law as

now here we know that enclosed charge in the inner shell is ZERO
so we have


Now for the position between two shells

again by Gauss law

now here we know that enclosed charge between two shells is given as

so we have


Now for position outside the shell we will have

again by Gauss law

now here we know that enclosed charge given as

so we have


Part b)
If outside the shell net electric field is zero
then we can say



Part c)