3 6 9 12 15 18 21 24 27 30 
3 6 9 10 12 15 18 19 21 24 25 27 30 
3 6 9 10 12 15 18 19 21 24 25 27 30 
lower on 9 9
lower on 13 15
upper on 9 10
equal range
first 9
second 10