a$)$ What should the minimum self$-$cleansing velocity of a gravity pressure system be$?$

b$)$ Assuming a pipe roughness of ks $=1\mathrm{.}5$ mm$,$ what should the pipe on$-$grade capacity be of a pipe of internal diameter $375$ mm set in a gradient of $1$: $200?$

c$)$ During Peak Wet Weather Flow $($PWWF$),$ what is the maximum allowable velocity in gravity sewers and state the reason for this limitation$?$