$12-9.$ Six pound moles of ethane, three $lb$ moles of propane and one $lb$ mole of n$-$butane are mixed in a closed container and the temperature is adjusted to $75F.$ What is the bubble$-$point pressure? What is the dew$-$point pressure? Calculate the compositions of the gas and liquid at equilibrium at $75F$ and $300$ psia.

$12-10.$ Determine the compositions of the gas and liquid phases of the mixture in Exercise $12-9$ at $75F$ and $5000a.$ What do your results indicate about the phase of this system?