Well, after an extensive search, I have found nothing correlating GRASS with the density of solids. I do have some answers for you on calculating density, however.
Density of anything is the mass per given unit of volume. This basically is a physical characteristic of the substance, it has so much matter in a given volume unit. If the solid you are measuring has a linear arrangement, with length, width and height measurements, you can simply measure those, multiply them times each other, like this:
L x W x h = Volume, usually in cubic centimeters or cubic meters
Place the object on a measuring scale for mass to get the number of grams or kilograms of mass the object contains. Then use the two numbers you have just calculated in the density formula:
D = m/V, or Density = mass/Volume
You will get so many grams per cubic centimeter, or in the case of larger objects, kilograms per cubic meter.
If the object is irregularly shaped, get the mass of the object as we did above, either in grams or kilograms. Then submerge the object in water and collect the amount of water overflow the object displaces. Measure the volume of the water displaced, then use that number as your volume measurement. Substitute the numbers into the density formula as you did above, and calculate the density of the object.
I found out the answer from my teacher. Grass is an acrostic and is used for answering questions in science.