Question

If A is a subset and equal to B then B'-A' is equal to​

Answer 1

A-B

Explanation:

It doesn't say A=B... But just that A is a subset of B.

Anyways, why not try an example to help reveal the answer.

Let the universe set, U, be U={1,2,3,4,5,6}.

Let B={1,2,3,4} and A={1,3,5}

First choice would become A'={2,4,6}

Second choice would become B'={5,6}

Third choice would become A-B={5}

Fourth choice is just { }

B'-A'={5}

The only choice matching is A-B

*Just so you know X-Y is the set of elements contained in X only if they are not also in Y.