which one's are proportional, which one's are not?

1. 3/7 = 6/8

2. 2/5 = 10/24

3. 9/21 = 3/7

4. 10/12 = 2/8

5. 25/15 = 5/3

6. 12/4 =9/3

7. 11/12 = 8/13

8. 21/ 7 = 6/2