A fish meal contains oil that has to be extracted with benzene operating in multiple stages in direct current. Experimentally it has been found that the solution retained by the inert solid is a function of the composition of the solution.

$1000$ kg$/$h of feed containing $40\%$ by weight of oil enters the extraction system, which consists of $3$ stages, and the amount of benzene used in each stage is $750$ kg$.$

Calculate

a$)$ the overall composition of the extract or upper flow