Answer:
I believe it would be 6 hearts to 9 stars
Explanation:
explanation #1
4 hearts to 6 stars can be reduced, which makes 2 hearts to 3 stars. so you go from 2 hearts : 3 stars to 4 hearts : 6 stars then you would get to 6 hearts : 9 stars.
explanation #2
4:6 can be reduced which equals 2:3. the difference between 2 and 4 is 2 and the difference from 3 and 6 is 3. so 6:9 would be after 4:6
hopefully this helps!