Please can u explain this ...?

Methanol, CH3OH, is sometimes used as an antifreeze for the water in automobile windshield washer fluids. How many grams of methanol must be added to 4.90 kg of water to lower its freezing point to -17.0�C? For each mole of solute, the freezing point of 1 kg of water is lowered 1.86�C.