M = moles of solute / kgsolvent written like this:
So again, Molality problems are simply ratio of fraction set equal to each other where one ratio you have all the information (known ratio) and the second ratio where you are missing information. When you are determining the amount of solvent or solute needed to create a given molality (m) solution, you will need to show the units of m as its component (mole solute chemical formula / 1 kgsolvent) so that you are showing units canceling.