If 42.9 mL of rubbing alcohol is dissolved in water to make 215 mL of
solution, what is the concentration
expressed in volume/volume % of
the solute?

19.8 %

Explanation:

V% = ( V of solute \ 100 ml  of solution ) ×100%  =

   the volume of the solute in 100ml solition = 20 ml

  42.9 ml of solute 215 ml solution

     ×                      100 ml solution

42.6 ×   100 ml  ÷ 215 ml

= 19.8 ml of solute

the V% =   (19.8 ÷ 100)  ×100% = 19.8%

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.