A feed with $40\%$ ethylene glycol, $55\%$ water and $5\%$

of furfural is mixed with pure furfural $($solvent$)$ in a system

in countercurrent. It is necessary to produce a refined product with

maximum concentration of $3\%$ ethylene glycol, and an extract with

minimum concentration of $50\%$ ethylene glycol. The system is

carried out under conditions of $25$ C and $1$ atm. How many stages are there

necessary for this process?