An aqueous solution has a freezing point of -0.670. what is the molality of the solution?

Calculate a new concentration of buffer with the pH of 4.91 for 3.907mL of 1.0 M acetic Acid and 6.093mL of 1.0 M Sodium acetate and 90mL water with an addition of 2.90mL of 1.00 M NaOH is added. calculate a new concentration of acid and base. assuming you don't know the initial concentration of acid and base.

there are 3 ways to solve this.

1. assume that both of the acid and base concentration are correct

2. assume that only one of the concentration is correct.

3. assume that none of the concetration are corrected. (and this is what I want to solve, by the third method)