Chapter 9, Problem 9.111E

How would the $\text{pH}$ values of equal molar solutions of the following salts compare (highest, lowest, etc.)? ${\text{NaH}}_{\text{2}}{\text{PO}}_{\text{4}}$, ${\text{Na}}_2{\text{HPO}}_{\text{4}}$ and ${\text{Na}}_3{\text{PO}}_{\text{4}}$.