Answer: The volume of ethyl alcohol contained in 35 mL (1 oz.) of 86-proof liquor is 15 mL.
Explanation: 86 proof liquor means that it has 43% alcohol by volume (v/v).
This means that 43% of the volume of the liquor is alcohol, and 57% is other substances.
In a 35 mL bottle of liquor, this means that there are 0.43 x 35 mL = 15 mL of alcohol.
So the answer is 15