x is a multiple of 6 and 1 ≤ x ≤ 16

x is a multiple of 6 and 1 ≤ x ≤ 16.

We want multiples of 6 between 1 and 16.
We start with 6.
Another multiple of 6 is 12
The next multiple of 6 is 18, which is out side the range of 1 ≤ x ≤ 16.

So our number set is x = {6, 12}