In $5$ PFR reactors connected in series, two gases A and B react with liquid C which occupies a negligible volume in the reactor. the reaction

the elementary

A$+$B$+$C$->$R Inert material is the same in the feed as CAo $=$ CBo$=0\mathrm{.}1$ mol$/$l$,$ CCo$=10$ mol$/$L$,$ k $=11($L$/$mol$)$

L$/$mol $0\mathrm{.}4=$ClO. What is the dwell time required to reach $0\mathrm{.}8=$ XA after the fifth reactor?