15. [MSW] Pentane (C5H12,MW=72.15g/ mole ) and hexane (C6H14,MW=86.17 g/mole) form an ideal solution. At 25C the vapor pressures of pure pentane and pure hexane are 511 torr and 150 torr, respectively. The mole fraction of pentane and hexane are 0.720 and 0.280, respectively. What is the vapor pressure of the solution? a. 133 torr b. 368 torr c. 661 torr d. 410 torr e. None of the above