How do I use the molality of a substance to calculate the molar mass?       Example: molality is .122M of an unknown substance. I have the mass of the unknown solute (.346 g), and the mass of the...

How do I use the molality of a substance to calculate the molar mass?       Example: molality is .122M of an unknown substance. I have the mass of the unknown solute (.346 g), and the mass of the solvent (7.79 g).