It's January in Nashville and your local weather station just informed you that the temperature outside is -8.9 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 is 8.9.
i = 2 (because NaCl breaks into two ions)
Kf = 1.86 degrees/molal
calculate molality = m

molality = mols/kg solvent
You know molality, you know kg solvent, calculate mols.

mols = g/molar mass
you know mols from above, molar mass NaCl is about 58.5 (but you should get the exact number), calculate grams NaCl, then divide by 1000 to convert to kg NaCl.
Post your work if you get stuck.

Answer 2

I forgot to mention that the amount calculated this way will provide the kg NaCl to lower the freezing point of water to -8.9 degrees C at which point both ice and water can co-exist. It will take a smidgen more to make sure it all melts.