still residue composition

A batch distillation column with eight theoretical stages (the first stage is the still pot) is charged with 500 kmol of a 48.8 mol% A in B mixture at atmospheric pressure (relative volatility aAB = 2.0). The boil-up ratio is constant at 213.5 kmol/h. If the distillate composition is to be maintained content at 95 mol% A by varying the reflux ratio, calculate the distillation time required to reduce the still residue composition to 19.2 mol% A. Calculate the fractional recovery of A in the distillate.