How Many Moles of Solid NaF Would Have to Be $\times$

Multiple Choice

How many moles of solid NaF would have to be added to 1.0 L of 2.39 M HF solution to achieve a buffer of pH 3.35? Assume there is no volume change.(K_a for HF = 7.2 $\times$ 10^-4)

A) 3.9
B) 0.50
C) 0.67
D) 1.0
E) 1.6