180
The least common multiples of the number 6 and 9 is 3.
The common multiples of 4 and 9 are 36, 72, 108 and so on.
Not all of them are. Consider 27. 6 and 9 share a lot of common multiples because they share a common factor.
Multiples of 90
lcm(4, 9) = 36 → the two least common multiples (ie the first two common multiples) of 4 and 9 are 36 and 72.
36, 72 and 108.
18, 36, 54, 72
There are plenty of common multiples, but only one can be the least; thus the least common multiple of 3, 6, 9 is 18.
18