n=12.5
Those are equivalent fractions. What you do to the numerator you do to the denominator. Now you can actually reinterpret this as a ratio.
10:8
n:10
So to get the 8 to ten you can divide by 8 and multiply by ten, correct?
Then you do the same to the ten, 10 divided by 8 multiplied by ten which will give you 12.5.
Hope this helps you.