Question 1026954
Since E∪F = (E-F)∪(E∩F)∪(F-E), and each of the three components are mutually exclusive, it follows that.

n(E∪F) = n(E-F) + n(E∩F) + n(F-E) = 12 + n(E∩F) + 30 = 42 + n(E∩F)

==> n(E∪F) = 42 + n(E∩F) ≥ 42.

n(E∪F) = 42 only when E∩F = ∅.