A 50.0 mL solution of NH3 was titrated with 0.100 M HNO3. The volume of titrant required to reach the equivalence point was determined to equal 38.25 mL (Kb = 1.8 x 10^-5). what is the pH of the solution after 20.0 mL of HNO3 were added?
a. 4.78
b. 9.22
c. 9.29
d. 10.84
e. 11.16