Verified answer

Well, draw the diagram and label your sets with element counts.

That's a rectangle containing two separate circles.

You have 48 in circle A.

You have 48 + 43 in the entire rectangle (U).

From the basic identity

n(B) + n(B') = n(U)

You can derive n(B), completing your labels.

Now,

n(A∪B) = n(A) + n(B), since they're disjoint sets.