They are the first three multiples of their lowest common multiple: 36, 72, 108.
A common multiple of 3 and 4 is a number which is a multiple of 3 and of 4. The first 3 common multiples of 3 and 4 are 12, 24, 36
4, 8 and 12 are the first 3 common multiples of 2 and 4
The first three multiples of 4 are 4, 8 and 12. For them to be common, they need to be compared to another set of multiples.
The first 3 common multiples of 4 and 12 are: 12, 24, 36
They are: 6 12 18 and 24
8,16,24
12,24,36