If universal set = N, the set of natural numbers, set A = {multiples of 3 less than or equal to 20}
and
Set B = {multiples of 4 less then or equal to 20}, then A - B is equal to :

1. {3, 6, 9, 15, 18}

2. {4, 8, 16, 20}

3. {0}

4. {12}

Find all the subsets of A = {5, 7} .

Find all the subsets of C = {x : x ∈ W, x ≤ 2} .

Find all the subsets of {p : p is a letter in the word 'poor'} .