Density is mass/volume. The mass is given, 32g. To calculate volume, you need to multiply 4*2*3, which is multiplying length, width, and height.
4*2=8
8*3=24
To calculate density, you divide the mass (32) by the volume (24).
32/24= 1.3333333...
Your answer, depending on the person, would either be 1.33, 1.3, 1.33 with the line about the 2 3s, or 1 1/3. Hope this helps! Also, remember to label it g/cm2.