The PK_a's of the Three Acid-Conjugate Base Pairs Derived from Phosphoric

The pK_a's of the three acid-conjugate base pairs derived from phosphoric acid, H₃PO₄, are 2.12, 7.21 and 12.32. How many g of sodium hydroxide would have be added to 150 mL of 0.1 M H₃PO₄ to prepare a buffer of pH = 7.41?

A) 0. 21 g
B) 0.34 g
C) 0.56 g
D) 0.83 g
E) 0.91 g