How Many Mmoles of HCl Must Be Added to 155

Multiple Choice

How many mmoles of HCl must be added to 155.0 mL of a 0.28 M solution of methylamine (pK_b = 3.36) to give a buffer having a pH of 11.42?

A) 19 mmol
B) 0.17 mmol
C) 6.2 mmol
D) 3.7 mmol
E) 0.61 mmol