The operator has to make a decision for a case in a water treatment plant. In this plant, salt concentration in a tank with a volume $32000$ L is required to be decreased from $30000$ mg$/$L to $1000$ mg$/$L$.$ This reduction can be achieved via two ways $(1$st option$)$ The tank will continously flushed with a salt$-$free flow of $240$ L$/$day $(2$nd option$)$ Initially, a portion of the salty water in the tank will be discharged and then the tank volume can be re$-$filled with a salt$-$free clean water in order to obtain a salt concentration of $1000$ mg$/$L$.$Tha allowable maximum discharge and inflow flowrates are $240$ L$/$min and $400$ L$/$min$,$ respectively. If the operator wants to reduce salt concentration within the minimum time, which option is the most feasible one?