A buffer is prepared by mixing 100.0 mL of 0.200 M acetic acid (HC₂H₃O₂) with 60.0 mL of 0.100 M NaOH. The pKa of acetic acid at 25 °C is 4.74. After the buffer is formed, 5.0 mL of 0.100 M HCl is added with no change in temperature. What is the pH of the solution after the HCl addition?
a) 4.74
b) 5.16
c) 4.32
d) 4.22