6 itself is a multiple of 3, so any multiple of 6 is also a multiple of 3. We can
ignore the 3, and just find a number that's a common multiple of 4 and 6.
The way I do that is to investigate the multiples of 6, and just keep going until
I find one that's also a multiple of 4.
-- First multiple of 6 . . . 6. No, that's not a multiple of 4.
-- Second multiple of 6 . . . 12. Yes ! That's a multiple of 4.
So the least common multiple of 3,4,and 6 is 12.
After that, of course, multiples of 12 are also multiples of 3, 4, and 6, as well as
multiples of other numbers.
The 6 smallest multiples of 3,4, and 6 are ...
12, 24, 36, 48, 60, and 72 .