A secondary treatment system has an aeration tank with a volume of $5,000$m$^3$ and operates with a MLSS concentration of $3,800$ mg $/$ L$.$ If $3\mathrm{.}200$kg of secondary solids are produced each dav, then what is the solids retention time $($hr$)?$ Select the value nearest to the answer. $4.961405,900140,000$