Let A= {2, 4, 6,8, 10, 12}, B = {3, 6, 9, 12}. How many subsets of B are not subsets of A ?
Let us find out how many subsets of B are subsets of A. For this, we must find A and B's intersection, {6,12}. The number of subsets of this set is $$2^2=4$$. Now, find the total subsets of B.
$$2^n\ where\ n\ is\ no.\ of\ elements$$
$$2^4=16$$
The answer is to subtract the four subsets that are in common with A and B. 16 - 4 =12.