A volume of $x \mathrm{~mL}$ of $5 \mathrm{M} \mathrm{NaHCO}_3$ solution was mixed with 10 mL of $2 \mathrm{MH}_2 \mathrm{CO}_3$ solution to make an electrolytic buffer. If the same buffer was used in the following electrochemical cell to record a cell potential of 235.3 mV , then the value of $x=$ $\_\_\_\_$ mL (nearest integer). $$ \mathrm{Sn}(\mathrm{~s})\left|\left[\mathrm{Sn}(\mathrm{OH})_6\right]^{2-}(0.5 \mathrm{M})\right| \mathrm{HSnO}_2^{-}(0.05 \mathrm{M})\left|\mathrm{OH}^{-}\right| \mathrm{Bi}_2 \mathrm{O}_3(\mathrm{~s}) \mid \mathrm{Bi}(\mathrm{~s}) $$ Consider upto one place of decimal for intermediate calculations