A food chemist determines the concentration of acetic acid in a sample of apple vinegar by acid-base titration. The density of the sample is 1.01 g/mL. The titrant is 1.017 M NaOH. The average volume of titrant required to titrate 25.00 mL subsamples of the vinegar is 20.78 mL. What is the concentration of acetic acid in the vinegar? Express your answer the way a food chemist probably would: as percent by mass