0.4 g mixture of $\mathrm{NaOH}, \mathrm{Na}_2 \mathrm{CO}_3$ and some inert impurities was first titrated with $\frac{\mathrm{N}}{10} \mathrm{HCl}$ 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 $\mathrm{Na}_2 \mathrm{CO}_3$ in the mixture is $\_\_\_\_$ (Rounded-off to the nearest integer)