Listerine mouthwash has 21.6% ethyl alcohol by volume. What mass of ethanol is contained in 20.0 mL of mouthwash ?! ( the density of ethanol is 0.789 g/mL.)

If that is 21.6%(v/v), it means 21.6 mL EtOH/100 mL soln; therefore, 20 mL will contain
21.6 mL EtOH x (20 mL/100 mL) = ?? mL EtOH.
Then mass = volume x density.