Density of something relates the mass to the volume and will have units of mass/volume. So, somewhere in your text or in a reference or online, you should be able to find the density of gold. With that, you can use the following relationship:
density = mass / volume or d = m/v
You'll just rearrange that equation to have mass on one side like:
m = d X v
So, if you multiply the density (in units of g/cm^3) by 20 cm^3, you will calculate its mass.
