The density is 1g/cm³. To calculate density, the equation density=mass/volume is used. You already know the mass, 27g, but you need the volume. The equation for volume is length x width x height. Plug in your side measure 3, to get 3 x 3 x 3, which is 27cm³. Now, just divide the mass by the volume. 27g/27cm³= 1g/cm³
