You Are Titrating a Solution of Sodium Hydroxide of Unknown

You are titrating a solution of sodium hydroxide of unknown concentration with a solution of phosphoric acid that has a concentration of 0.300 M. Starting with 29.0 mL of the sodium hydroxide solution, you use 16.8 mL of the acid to titrate the base to completion. Calculate the concentration of the sodium hydroxide solution.

A) 0.518 M
B) 0.174 M
C) 0.0579 M
D) 0.521 M
E) 0.348 M