The elementary irreversible aqueous$-$phase reaction A$+$B$->$R$+$S is carried out isothermally as follows. Equal volumetric flow rates of two liquid streams are introduced into a $4-$liter CSTR$.$ One stream contains $0\mathrm{.}020$ mol A$/$liter$,$ the other $1\mathrm{.}400$ mol B$/$liter$.$ The mixed stream is then passed through a $16-$liter PFR$.$ We find that some R is formed in the CSRT$,$ its concentration being $0\mathrm{.}002$ mol$/$liter$.$ Find the concentration of R at the exit of the PFR as well as the fraction of initial A that has been converted in the system.