$9.$ In a continuous contact extractor, if the flow rate of the solvent is $100$ mL$/$min and the operation lasts for $2$ hours, what is the total volume of solvent used?

$10.$ A batch extractor operates with a mixture that contains $30\%$ solute and $70\%$ solvent by weight. If the total weight of the mixture is $200$ g$,$ how much solute is present?

$11.$ For a ternary system, if the composition of component A is $20\%$ and component B is $30\%,$ what is the composition of component C$?$

$12.$ In a counter$-$current extraction setup with a distribution coefficient of $2,$ if $100$ g of solute is initially present in the aqueous phase, how much solute will be in the organic phase after one stage?