A beaker contains 450 g of water if 9.2g of calcium fluoride is added what is the molality concentration of the solution

Molality = moles of solute / kg of solvent

You need to switch the units you have to fit the formula so

450 g =.45 kg

9.2 g / 40.078 g =.2296 moles of calcium

.2296 moles /.45 kg =.51 m

The concentration is. 51 m