500 mL of 0.1M HCl is mixed with 500 mL of 0.02M HA (weak acid) solution. To this solution, 2 g of solid NaOH is added. What is the pH of the resultant solution?
(Given} \( K_a \) of HA is \( 4 \times 10^{-10} \), molar mass of NaOH is 40 g/mol, log 2 = 0.3, log 4 = 0.6\bf{)