It's January in Nashville and your local weather station just informed you that the temperature outside is -4.37 degrees Celcius. You estimate the amount of ice on your driveway to be approximately 30kg. What is the minimum amount of sodium chloride in kilograms (kg) needed to lower the freezing point of the water so that the ice melts

Answer 1

delta T = i*Kf*m
delta T = 4.37 C. You might want to make that 4.38 to add just a wee bit more.
i for NaCl = 2
Kf for water = 1.86
Substitute and solve for m = molality

Then m = mols/kg solvent
You know m and kg (30) solvent. Solve for mols.

Then mol = grams/molar mass
You know mol and molar mass, solve for grams.