Let u = {all integers}. consider the following sets: a = {x | x ∈ u and x > 3} b = {x | x ∈ u and x is an even integer} c = {x | x ∈ u and 2x is an odd integer} d = {x | x ∈ u and x is an odd integer} assuming 0 is an even integer, which set is the complement to set b? which set is an empty set? which set would contain the subset e = {1, 3, 5, 7}?