What is the molarity of 0.60N $H_3PO_4$ (a tribasic acid)in the following reaction?$H_3PO_4+2OH^-\rightarrow HPO_4^{2-}+2H_2O$

Question

$\begin{array}{1 1}(a)\;0.30M\\(b)\;0.40M\\(c)\;0.90M\\(d)\;0.15M\end{array}$