Explanation:
B ∩ C means the values of z that are in both sets (every z that is smaller than 1 AND larger or equal to 5).
I don't think it is a big surprise that they're is no such value, and the result is the empty set
B ∩ C = ∅
B ∪ C means the values of z that are either smaller than 1 OR larger or equal than 5.
in other words : the union of both sets.
B ∪ C =
(-infinity, 1) ∪ [5, +infinity)