12. divide by 15 to get 1/4 13. divide by 2 to get 16/20 14. divide by 10 to get 8/10 15. divide by 5 to get 7/9 16. divide by 15 to get 1/5 17. divide by 8 to get 4/6 18. divide by 2 to get 9/16
Are you ok on the rest? And let me know if you need more help
