$(12)$ Two circular sedimentation basins, each $30m$ in diameter and $3m$ deep, settle a total flow of $3800\frac{m^3}{d}$ in a primary system. Draw and label a sketch of this system and calculate $($a$)$ the detention time, $($b$)$ the overflow rate, $($c$)$ the critical settling velocity, and $($d$)$ the flow rate over the effluent weir.