What Is the PH of the Buffer That Results When $\times$

What is the pH of the buffer that results when 12.0 g of NaH₂PO₄ and 8.00 g of Na₂HPO₄ are diluted with water to a volume of 0.50 L? (K_a of H₂PO₄^- = 6.2 $\times$ 10^-8,the molar masses of NaH₂PO₄ and Na₂HPO₄ are 120.0 g/mol and 142.0 mol,respectively)

A) 4.10
B) 6.96
C) 7.21
D) 7.46
E) 9.90