$**$Just need the asnwer to question $7**$

The manufacturing process that generates the waste in the previous CMFR problem $($Q$5)$ is shut down, and now starting at

$t=0$ the pollutant concentration entering the CMFR is zero. How many days $($answer to $1$ decimal point$)$ does it take the

tank concentration to reach $10$ percent of its initial steady$-$state value?