b$)$

A channel$-$type grit chamber has a flow$-$through velocity of $0\mathrm{.}3$ m$/$s$,$ a depth of $0\mathrm{.}8$ m$,$ width of $0\mathrm{.}7$ m and a length of $15$ m$.$ The grit chamber can treat $5$ MLD$.$ Find the setting velocity of particles which can be removed with $100$ percent efficiency. What is the detention period of the chanber