A liquid feed to a distillation tower at $405\mathrm{.}3$kPa abs is fed to a distillation tower. The composition in mol fractions is as follows: $n-$butane $)=(0\mathrm{.}40n-$pentane $)=(0\mathrm{.}25,n-$hexane $)=(0\mathrm{.}20-$heptane $)=(0\mathrm{.}15.$ Calculatd the boiling point and the vapor in equilibrium with the liquid.