Some municipalities add fluoride into drinking water to improve dental health $($e$.$g$.,$ help

prevent tooth decay$).$ Due to a major storm event, the fluoride feeder at a drinking water

treatment plant ran out of feed solution. The fluoride feed tank $($described as a CMFR$)$ is

connected to a $6-$km distribution pipe $($behaving as a PFR$).$ The volume of the fluoride tank

is $2\mathrm{.}1m^3.$ If the concentration of fluoride in the feed tank solution is $1\mathrm{.}43m\frac{g}{L},$ how long

until the concentration of fluoride is reduced to $0\mathrm{.}02m\frac{g}{L}$ at the end of the distribution

pipe. Fluoride can be assumed as a conservative compound $($i$.$e$.,$ non$-$reactive$).$ Hint:

consider this as a two$-$part problem where you have two types of reactors that are

connected in series $($output from the $1^{st}$ reactor is input for the $2^{nd}$ reactor$).(8$ pts$)$