They are not in proportion, since its 6:9 round it down (2:3) so pretend the 6 are apples and the 9 are oranges
Every 2 apples there are 3 oranges
So having 9 apples what is that?
2 x ? = 9
2 x 4.5 = 9
So if you want to keep 2:3 you have you times the oranges by 4.5 aswell!
3 x 4.5 = 13.5
So since it is 9:12 not 9:13.5 they are not in proportion
