To solve this problem you must follow the steps below:
You have a/b=8/15, Then:
1. You must divide in both side of the given proportion by 8:
a/bx8=8/15x8
2. When you simplify, you obtain:
a/8b=1/15
3. Now, you must multiply both sides by "b", as below:
axb/8b=1xb/15
4. Finally, when you simplify, you have:
a/8=b/15