Calculate the pH at the following points in a titration of 40.0 mL

Calculate the pH at the following points in a titration of 40.0 mL of 0.100 M benzoic acid(K a =6.3×10 -5) with 0.200 M KOH.1. 10.0 mL of KOH solution added2. 15.0 mL of KOH solution added3. At the equivalence point. Verify any assumption you made.4. 21.0 mL of KOH solution added