$($a$)$ A $0\mathrm{.}290$ kg s$-1$ solution of $25\mathrm{.}0$ wt $\%$ dioxane in water is to be extracted using

benzene. The equilibrium distribution coefficient KD is $1\mathrm{.}20.$

Determine the mass flow rate of benzene required to extract $90\%$ of the

dioxane, using the following configurations:

$($i$)$ two countercurrent stages; $[4$ MARKS$]$

$($ii$)$ two crosscurrent stages using equal amounts of benzene.