Answer:
1 2/3 aka 1.6666666666666...
Explanation:
When you divide 15 by 9 that is the number you get, and you can verify it by then multiplying 9 by 1 2/3 and you get 15. I don't know if they are wanting you so get x, but if they do then you would multiply 6 by the scale factor and you would get 10.