The directions on a bottle of vinegar say "mix 1 cup of vinegar with 1 gallon of water to make a cleaning solution". the ratio of vinegar to water is 1 to 16. how many fluid ounces of vinegar should be mixed with 80 fluid ounces of water to make the cleaning solution?

The ratio for this is 1:16, with the amount of water being 16 times more than the amount of vinegar.
If the water has a volume of 80 fluid ounces, then the vinegar will be 80/16. This = 5 so the amount of vinegar in this ratio to make this cleaning solution is 5 fluid ounces. In other words, 5:80
Hope this helps :)