please solve

A liquid stream consisting of 12.0 mole% n-butane and the balance a heavy nonvolatile hydrocarbon is fed to the top of a stripping column, where it is contacted with an upward-flowing stream of nitrogen. The residual liquid leaves the bottom of the column containing all of the heavy hydrocarbon, 8.0% of the butane entering the column, and a negligible amount of dissolved nitrogen. Product gas ng (mol/time) T (C), 1 atm Feed liquid (mol/time) po mole% butane T(C) with STRIPPING COLUMN P= 1 atm Pb = 12.0 Pr = 8.0 T= 29.0C Feed gas ng, (mol/time) pure N2 Stripped liquid 1.2 (mol/time) p,% of entering butane The highest possible butane mole fraction in the exiting gas is that in equilibrium with the butane in the entering liquid (a condition that would require an infinitely tall column to achieve). Using Raoult's law to relate the mole fractions of butane in the entering liquid and exiting gas, calculate the molar feed-stream ratio (mol gas fed/mol liquid fed) corresponding to this limiting condition. n nt =