please solve D.15 and D.16 in details.

important note : the pressure in D.15 is 1000KPa not 100KPa

D15.* We have a flash drum separating 50.0kmol/h of a mixture of ethane, isobutane, and n-butane. The ratio of isobutane to n-butane is held constant at 0.8 (that is, zict I znC4=0.8 ). The mole fractions of all three components in the feed can change. The flash drum operates at a pressure of 100kPa and a temperature of 20C. If the drum is operating at V/F=0.4, what must the mole fractions of all three components in the feed be? D16. A feed that is 50.0mol% methane, 10.0mol%n-butane, 15.0mol%n-pentane, and 25.0mol%n-hexane is flash distilled. F=150.0kmol/h. Drum pressure =250.0kPa, drum temperature =10C. Use the DePriester charts. Find V/F, y V and