First three common multiples of 15 and 20 would be: 60,120,180
Since 3 is a factor of 15, the first three common multiples of 3 and 15 are 15, 30, and 45.
15 & 20 have an infinite number of Common Multiples; the first three are 60, 120 and 180.
15, 30, 45
15, 30 and 45
15, 30, 45
15, 30, and 45 are.
135, 270, 405
15, 30, 45
60, 120, 180
30 60 90
60, 120, 180