No$.8-2$

A shallow river with a mean flow rate of $2\mathrm{.}0$ miles per hour is in equilibrium with atmospheric oxygen immediately upstream of a waste outfall creating a BOD$0$ of $21$ mg$/$L immediately downstream. $($a$)$ If KBOD is $0\mathrm{.}2/$day and KOX is $1\mathrm{.}4/$day$,$ how far downstream was the maximum DO sag found to occur? $($b$)$ If the minimum DO in the river was determined to be $7\mathrm{.}3$ mg$/$L$,$ what was the prevailing water temperature?