Hello, I've been two days trying to resolve this problem and I can't. I will try to translate it. To liquid, A and B have very similar boiling point. Because of that would be separate by liquid-liquid extraction with a dissolvent C. Calculate the minimum quantity of extract we have to return of the product of extract and the refined quantity to obtain a 82% A 17% B extract ( solvent free basis) and 10% A 90% B refined ( solvent free basis too). Feed is 35% A, 65 % B ( solvent free) and it is a saturated refined. Calculate the ideal number of stages at the both sides of feeding with the same feed to get the same final product when the reflux relation (on kg of extract with solvent) / kg of extract product is the double of the minimun value The feed is 1000kg . Do on equilateral triangle, rectangle triangle and solvent free coordinate graph. Thank you very very much.