0.4 g mixture of $NaOH$, $Na_2CO_3$ and some inert impurities was first titrated with ${N \over {10}}$ $HCl$ using phenolphthalein as an indicator, 17.5 mL of $HCl$ was required at the end point. After this methyl orange was added and titrated. 1.5 mL of same $HCl$ was required for the next end point. The weight percentage of $Na_2CO_3$ in the mixture is $\underline{\hspace{2cm}}$. (Rounded off to the nearest integer)