Consider a treatment system without solids recirculation and with the following characteristics: $$ Reactor volume: V $=9,000$ m $$ Hydraulic retention time: $0=3$ d Influent substrate: S$.=350$ mg$/$L $$ Biomass in the reactor $($MLVSS$)$: X $=173\mathrm{.}3$ mg$/$L $$ Yield: Y $=0\mathrm{.}6$ gVSS$/$gBODs $$ Endogenous rate: ka $=0\mathrm{.}06$ d$?$ Maximum specific growth rate: Imax $=3\mathrm{.}0$ d$\text{'}1$ Half$-$saturation coefficient: Ks $=60$ mg$/$L a$)$ Calculate the soluble effluent BOD concentration $($in mg$/$L$),$ after steady$-$state conditions have been reached in the system. $(10$ Marks$)$ b$)$ Calculate the mass of biological solids produced in kg each day. $(15$ Marks$)$