In a review seccion the I was given this problem. .74 L of .3 M NaOH is required to react completely with .36 L of an unknown triprotic acid. What is the initial molatiry of the original acid solution? In the problem so put H_3A to represent the unknown acid. But I'm not sure how she got that and how to solve the problem with that.
We need to know the mass of unknown acid to calculate its mass and after that determine the molar mass. So it is not possible to solve this problem with this information.