write an overall $($salt $+$ water$)$ mass balance. it will be a differential equation.$($c$)$ use the overall mass balance to eliminate qout from the salt balance. also, use$($c$)=$ w $+$ c to eliminate from your dynamic model. write the final dynamicmodel as$()$dcd t $=$with $$ representing algebraic $($not differential$)$ expressions. the only variables$/$pa$-$rameters that should appear in your final dynamic model are: the inputs w$($t$)$ andq$($t$),$ the output c$($t$),$ the parameters w $,$ V$,,$ and time t$.$