Proving in Set Theory

I have this question provided for us as an exercise.

I did two solutions. I'm not sure if any of them is correct. Please help, even a tip in proving this would be really appreciated.

If $A\subset B$ then all the elements of A is in B .

So $A-B$ is just collection of those elements of A which are not in B and it's just empty set

$B-A$ is just collection of those elements of B which aren't in $A$ . So it may contain s some elements as per their structure.

So $B*A = B-A$

And if you want to use the first prove then it will look like as

$A-B\subset A$ and $A\subset B$ so $A-B\subset B$ but if you take any element from $A-B$ then this process said that it must be in $B$ which is a contradiction and $A-B$ must be empty then