You cannot measure the mass of a solid with a graduated cylinder.
mulitiplying
You use a graduated cylinder to measure the volume of the rock with the water and the water without the rock
Density is Mass/Volume. Without a measure of volume you cannot calculate density.
If the object is fully immersed then density is (5)/(45-30) = 5/15 = 1/3 gm per mL (and since it is less than 1 the density of water, is it fully immersed without something holding it down?)
Use a Graduated Neutral Density Filter.
As a chemist I can tell you that there are a significant purpose differences between the two, though sometime masked in high school chemistry. In college you learn that the graduated cylinder are more specifically designed to measure volume of a liquid. The test tube is glass which is safer to do most chemical reactions in - meaning the test tube is not generally used for measurement but rather a container for liquids.
What do you want to measure - mass, weight, volume, density. There's no answer for "measure" without indicating what is to be measured.
Place the 12 sided figure into the graduated cylinder, then fill the cylinder with water. Take note of how high the water level is (W1) . Fish out the 12 sided figure without removing much of the water. Take note of how high the water level is now (W2). The volume of the 12 sided object equals the difference in water level (W1 - W2).
Without knowing the density of the substance it is not possible. Grams are a measure of mass, litres are a measure of volume.
Without knowing the density of the substance it cannot be known. Milligrams measure mass, centilitres measure volume.
Water does NOT have a volume of 1230 cm. It has a volume of 1230 cm^3 or 1230 mL 'cm' is a linear measure NOT a volume measure. Density = 122 g/cm^3 NOT 1.22 g , this is the weight of a mass. Remember density = mass/ volume. Algebraically rearrange mass = density X volume Hence Mass(g) = 1.22 g/cm^2 X 1230 cm^3 mass = 1500.6 g or 1.5006 kg. NB Please make sure you write the correct units!!!!!
It is quite simple if it is a regular shaped object like a cylinder or a cube. For example if you wanted calculate the volume of a cylinder you need to know the radius of the circular cross-section of the cylinder - this is the measurement from the centre of the circle, to the outer-edge and then multiply that by the height of the cylinder. For irregular shaped objects don't think there is a simple mathematical way if you don't know the density but you can always use water displacement to get a volume measurement. Just drop the object you want to know the volume off into a graduated cylinder partially filled with water - the amount the level rises will be roughly equal to the volume of the object you dropped in.