The partial water vapor pressure over the soulution of glucose (C6H12O6) in water is 715 torr at 100 degrees celsius. Find freezing temperature of this solution.

well, you certainly know the vapor pressure of water at 100C is 760 torr.

Partial pressure of water is in accorance with the mole ratio, so

715/760=moleswater/totalmoles

715/760=moleswater/(molessugar+molewater)

molality=molessugar/1000kgwater
molality=molessugar/(moleswater*18)

take the first equation, solve for moles sugar/moles water, put it in the second equation, and you should have it.