You transferred 20. mL of acetic acid solution to an Erlenmeyer flask and added 2 drops of phenolphthalein solution. You filled your buret with 0.10 M NaOH so that the initial buret reading was 1.96 mL. After titrating your sample tothe faint-pink phenol-phthalein endpoint, the final buret reading was 17.50 mL.

What is the concentration of the acetic acid solution?