Explanation
We are given the following:

We are required to determine whether the set is finite or infinite.
We know that a finite set is a set whose element(s) can be counted while an infinite set is a set whose element(s) cannot be counted.
The elements in our given set can be counted i.e. suppose S = {7, 18, 9, 6}; n(S) = 4.
Therefore, it is a finite set.