The elementary irreversible aqueous phase reaction A $+$ B $->$ R $+$ S is carried out isothermally as follow. Equal volumetric flowrate of two liquid streams are introduced into a $1$ ft$3$ mixing tank. One stream contains $0\mathrm{.}020$ mol A$/$li$,$ the other stream contains $1\mathrm{.}4$ mols B$/$li$.$ The mixed stream is then passed through a $4$ ft$3$ plug flow reactor. We find that some R is formed in the mixing tank, its concentration being $0\mathrm{.}002$ mol$/$li$.$ Hence, the mixing tanks acts as a backmix reactor. Find the concentration of R at the exit of the plug flow reactor as well as the fraction of initial A that has been converted in the system.