Alternatively, you could use the Henderson-Hasselbalch equation.
Since you're dealing with a buffer, which in your case is a solution that contains a weak acid, acetic acid, and its conjugate base, the acetate anion, in comparable amounts, you can use the Henderson-Hasselbalch equation to determine its pH.
Use the classic approach to determine the concentrations of the weak acid and of the conjugate base after the sodium hydroxide solution is added.
Since you add together
The reaction will produce the same number of moles of acetate ions as the number of moles of sodium hydroxide consumed. This means that you will get
Therefore, the solution's pH is