If the density of Platinum is 21.45G cm3 How much space would 107.25G take up?

As you know the density (21.45g/cm³) and the volume (225.0cm³) - the mass is just the density multiplied by the volume:

21.45 * 225 = 4826.25g = 4.8kg

However the density of platinum varies slightly depending on the concentration of other Platinum family metals, like Rhodium and Palladium