3, 6, 9, 12, 15 and just keep adding three till you get to 120.
15 & 20 have an infinite number of Common Multiples; the first three are 60, 120 and 180.
105, 120, 135
-105
120 and all the multiples of 120.
60, 120, 180
60, 120, 180
40, 80, 120
44
40, 80, 120
They are: 60 120 and 180
120, 240, 360
40, 80, 120 and so on.