A mixture of benzene $($B$)$ and toluene $($T$)$ containing $50\%$ benzene by mass is separated by distillation into two fractions. The mass fraction of benzene in the top stream is $95\mathrm{.}5\%$ B and a bottom product stream contains $10\mathrm{.}0\%$ of benzene fed to the column. The top $($overhead$)$ goes through a condenser and all the overhead is condensed completely $($called a total condenser$).80\mathrm{.}0\%$ of the feed by mass is the overhead. A portion of the condensate is returned to the column as reflux R$,$ and the rest is withdrawn as the final product D$.$ Take a basis of calculation of $1000$ kg$/$h for the feed.

Determine the mass flow rate of the D$.$