What is the ratio of 75 and 85?

A ratio is expressed as 75/85 or 75:85

These figures can be simplified by dividing by 5.

15/17 or 15:17

With the latter expression the ratio is commonly seen with one number reduced to 1.

So 15 : 17 can be expressed as 1 : 1.1333 or 0.8824 : 1