Stream consisting of 44.6 mole% benzene and 55.4% toluene is fed at a constant rate to a process unit that produces two product streams, one a vapor and the other a liquid. the vapor flow rate is initially zero and asymptotically approaches half of the molar flow rate of the feed stream. throughout this entire period, no material accumulates in the unit. when the vapor flow rate has become constant, the liquid is analyzed and found to be 28.0 mole% benz