Mass, Volume, and Density

Use the sliders to explore the density of each box. The blue boxes are unit volumes (they represent 1 ml) and can be used as "overlays" to approximate how much mass is in each unit.
What is the density for Box a when its volume is 4ml? What about when its volume is 10ml? How can you make the density of A and B the same? Is there more than one way?