what are thr proper subsets of (march,april, may)

Answer 1

The proper subsets of A:{b,c,d} contain any combination of b,c, d and nothing else, except b,c,d. That is A is not a proper subset of A.
For example, {b,c} is a proper subset of A, so is {a}.
For any set X which contains n elements, there are 2^n-1 proper subsets, including ∅, and excluding X itself. Therefore for set A with three elements, you should be able to find 2^3-1=7 proper subsets.