III. HOW TO REPRESENT AN ELEMENT / MEMBER OF SET

How do I write or declare an object or something as a member / element of a specific set?
To say "member" of a set of used notation "∈". To say "not a member" used the notation "∉".
For example:

If A = {2, 3, 5, 7, 11}, then:
2 contained in A, means that 2 members of A and written 2 ∈ A
7 contained in A, means the 7 members of A and written 7 ∈ A
1 is not contained in A, means 1 is not a member of A and written 1 ∉ A
6 is not contained in A, means that 6 is not a member of A and written 6 ∉ A
etc.

IV. ELEMENTS OF A SET OF NUMBER PASSED
To state the amount or number of members of the set used the notation "n (name set)"
For example:
A = {chicken, ducks, goats, cows}, the number of members of A = 4, and write n (A) = 4.
B = {2, 4, 6, 8, 10}, the number of members of B = 5, and is written n (B) = 5.