$($b$)$ If $K=\frac{0\mathrm{.}001}{d}ay?$

$4\mathrm{.}6.$ Given

Assuming the entire system has reached equilibrium:

$($a$)$ What is the distance that must be used between the inputs shown and the water

withdrawal such that the concentration withdrawn is $1m\frac{g}{1}?$

$($b$)$ Suppose that the distance from the lake outlet to the withdrawal cannot be more

than $20mi.$ What should be the new volume of the lake?