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
Unless I am misreading, the question, or don't know all of it, there can be an infinite number of similar shapes. Three are give to you at the bottom of this answer, but there are many more possibilities.
