How do I calculate the molarity of a titrated solution?

I am so confused. I ran three titrations using .980 grams of potium acid phthalate in 50 mL of distilled water. The titration volumes (mL of NaOH needed) were 47.8, 45.7, and 52.2. Now I am supposed to figure of the molarity of the solution, and I have no idea were to start.