$12\mathrm{.}10-1.$ A continuous countercurrent multistage system is to be used to leach oil from meal by benzene solvent. The process is to treat $2000$ kg$/$h of inert solid meal $($B$)$ containing $800$ kg oil $($A$)$ and also $50$ kg benzene $($C$).$

The inlet flow per hour of fresh solvent mixture contains $1310$ kg benzene and $20$ kg oil. The leached solids are to contain $120$ kg oil. Assume that constant underflow of N$=1\mathrm{.}85$ kg solid$/$kg solution. Calculate the exit flows and compositions and the number of stages required.