A wastewater stabilization tank with a cross$-$sectional area A$,$ m$2$ being filled up with a continuous supply of water flowing at a feed rate of Fi$,$ m$3/$s$.$ The liquid level in the tank is to be maintained at a desired height h$,$ m$.$ The effluent from the tank $($Fo$,$ m$3/$s$)$ is controlled by a centrifugal pump. The tank is open from the top. $[$You can answer using the audio record option$]$

Identify the following variables and provide supporting reason for your choice

$($i$.)$ State variables $[5$ marks$]$

$($ii$.)$ Manipulated Variables