$(50$ pts$)$ The elementary gas$-$phase reaction, $AB,$ takes place isobarically and isothermally in a PFR where $63\mathrm{.}2\%$ conversion is achieved. The feed is pure A$.$ It is proposed to put a CSTR of equal volume upstream of the PFR$.$ What will be the intermediate conversion from the CSTR$,x_1,$ and the exit conversion from the PFR$,x_2,$ considering that the entering flow rates and all other variables remain the same as that for the single PFR$.$