How would I do this?

[humble pasture]

I’m a little confused on how to do this and I guess this was made to test students understanding of set theory. I’m wondering if A prime intersection of B Prime does not include III?

[humble pasture]

And if it were to say give (A intersection of B) prime would that be everything because it’s asking for not the intersection of A and B and since there’s nothing there you would include everything but that which is 1,2,3,4?

[ashen shale]

let's try to break down the problem by just finding A' and B'
now, you found out A' earlier and that was 2,3,4 correct?
similarly, B' would be 1,3,4
now we can see what's common between them :
3,4.

[ashen shale]

yes the answer of that would be 1234