1. given the universal set u = {a, b, c, d, e, f, 1, 2, 3, 4, 5, 6, 7, 8, 9} let a = {a, b}, b = {a, c, 2, 4, 6}, c = {1, 2, 3, 4} and d = ∅. give the contents, cardinality value, or truth value of the following. a) |d| b) d ∈ a c) ~b d) a ∩ b e) (u – b) ∪ c f) c ⊆ b