Phosphoric Acid Is a Triprotic Acid in Water,ionizing in the Following

Phosphoric acid is a triprotic acid in water,ionizing in the following sequential steps: H₃PO₄ + H₂O $\leftrightarrows$ H₂PO₄^- + H₃O⁺ = 7.11 *10^-3
H₂PO₄^- + H₂O $\leftrightarrows$ HPO₄^2- + H₃O⁺
= 6.32 *10^-8
HPO₄^2- + H₂O $\leftrightarrows$ PO₄^3- + H₃O⁺
= 4.5 *10^-13
What is the pH of a 0.20 M Na₃PO₄ solution?

A) 1.66
B) 5.82
C) 10.50
D) 12.75
E) 12.82