Answer:

The individual members of a set are called its elements.

For example for the set A = {days of the week}, the elements of A are Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
For the set B = {prime numbers less than 16}, the elements of B are 2,3,5,7,11,13

The symbol ∈ is used to indicate that an object is an element of a set, so Monday ∈ A means Monday is an element of A.

The letter n before a set denotes the number of elements in the set, so n(A) = 7 and n (B) = 6.