please explain in detail

31.3-4. Countercurrent Multistage Leaching of Halibut Livers. Fresh halibut livers containing 25.7wt% oil are to be extracted with pure ethyl ether to remove 95% of the oil in a countercurrent multistage leaching process. The feed rate is 1000kg of fresh livers per hour. The final exit overflow solution is to contain 70wt% oil. The retention of the solution by the inert solids (oil-free liver) of the liver varies as follows, where N is kg inert solid/kg solution retained and yA is kg oil/ kg solution: Calculate the amounts and compositions of the exit streams and the total number of theoretical stages