What is the normality of 0.20M $H_3PO_4$ (a tribasic acid)in the following reaction?$H_3PO_4+2OH^-\rightarrow HPO_4^{2-}+2H_2O$

Question

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