Explanation:
2:3 and 4:6 is proportional because if you simplify 4:6 it will equal 2:3.
1:4 and 6:18 is not proportional because if you simplify you would not get 1:4.
3:5 and 1:3 is not proportional because you can't simplify it any further and they do not equal each other.
2:5 and 8:20 is proportional because if you take 2:5 and multiply each number by 4 you would get 8:20.
4:9 and 12:27 is proportional because you can simplify 12:27 and get 4:9.
6:15 and 2:5 is proportional because you can multiply 2:5 by 3 and get 6:15.