Use counting to determine the whole number that corresponds to the cardinality of these sets. ​
(a) a = ​{x|x ∈ n and 17 < x ≤ 23}, ​
(b) b =​ {x|x ∈ n and x − 5 =​ x},​
(c) c =​ {x|x ∈ n and ​(x − 88​) (x −22​) =​ 0} ,
​(d) d =​ {x|x ∈ ​n, 1 ≤ x ≤ 100 and x is divisible by both 77 and 22​}
n(A)=