You need at least two numbers to find an LCM.
42
42
30
It is: 42
12,24.36
The LCM is 30.
The answer that I got was 24, and any multiples of 24.
The LCM is: 12
42
The lowest common multiple is 384
42 is the LCM of 3, 6 and 7. All multiples of 42 are multiples of 3, 6 and 7
The common multiples of 5 and 6 are the multiples of their lowest common multiple (which is 30), so there are infinitely many common multiples of 5 and 6. The first five are: 30, 60, 90, 120, 150.