A solution was prepared in which 12.0 g of glycerin was dissolved in 80.0 g of water. The freezing point of the solution was -3.03 °C. Use this information to determine the molar mass of glycerin.
delta T = k*m
Substitute and solve for m = molality
m = mols/kg solvent.
Substitute and solve for mols.
mol = grams/molar mass.
You know mols and grams, solve for molar mass.