$6\mathrm{.}12$b$.$ Differential distillation with constant relative volatility

A $30$mol$\%$ feed of benzene in toluene is to be differentially distilled. A prod$-$

uct having an average composition of $45$mol$\%$ benzene is to be produced.

Calculate the amount of residue left, assuming that $=2\mathrm{.}5$ and $F=100$mol.

Answer: $W=57\mathrm{.}4$ moles