Answer:

20. 3

21. 10

22. 2

Step-by-step explanation:

The factors of 6 are: 1, 2, 3, 6

The factors of 9 are: 1, 3, 9

The factors of 20 are: 1, 2, 4, 5, 10, 20

The factors of 30 are: 1, 2, 3, 5, 6, 10, 15, 30

The factors of 12 are: 1, 2, 3, 4, 6, 12

The factors of 15 are: 1, 3, 5, 15