A mixture contains n-pentane, n-hexane, and n-heptane at equal mole fractions. The temperature is 55 °C.

a) Calculate the bubble and dew pressure at 55 °C. 

b) What is the phase of the system at 1.7 bar, 55 °C? If a two-phase system, calculate the amount and composition of each phase. 

c) Repeat the previous part at 0.5 bar. 

d) The pressure is adjusted so that 75% of the mixture is vapor while the temperature remains at 55 °C. Determine the pressure and the compositions of the two phases. 

Additional data: At 55 °C the vapor pressures of n-C₅, n-C₆, and n-C₇ are 1.903 bar, 0.644 bar, and 0.231 bar respectively.