60 and 120
The two common multiples of three and five are: 15 and 30 ^-^
30
60 and 120
The LCM is: 30
Since 30 is a multiple of 6, all multiples of 30 are common.
A single number cannot have common multiples, until you are comparing it with one or more other numbers.
One common multiple of 15 and 30 is 60. Want another? 120
They are: 30 and 60
15 and 30
30 and 60
Do you mean common multiples? If so, then 30, 60, 90 etc. are common multiples of 30 and 5. If you mean multiples of 5 and factors of 30, that's 5, 15 and 30.
20 and 30 could be two such numbers.