The pressure$-$composition diagram of a nearly ideal hexane$+$heptane mixture at $70C$ is given.

Consider a system of global composition $50\%$ hexane and $50\%$ heptane $(($:$Z_{heptane}=0\mathrm{.}5\}.$

Describe the system $($number and nature $(L$ or $V)$ of phase$($s$),$ composition in heptane of individual phases if more than one, and proportions of the phases if more than one$)$ at the following pressures: $700,550$ and $300$ torr.