Sunlight and gravity are not considered matter because sunlight does not have a rest mass that is characteristic of matter while gravity is just a vector component of matter.
<u>Explanation:</u>
Sunlight has energy and momentum that makes it similar to matter but it cannot be considered matter when you consider all the factors that are characteristic of matter. Light is an electromagnetic wave that is made up of photons and the protons do not have rest mass.
Gravity is a vector component of matter that has both magnitude as well as direction and the gravity increases with increase in mass of an object.
Take into account that density and relative density are given by:

Take into account that the volume associated to each of the given sustances in the table is determined by the Level Difference (because it is the change in the volume of the water of the recipient in which the substance is immersed).
The density of water in kg/m^3 is 1000 kg/m^3.
Due to the density must be given in kg/m^3, it is necessary to express the volumes of the table in m^3 and mass in kg, then, consider the following conversion factor:
1 m^3 = 1000000 ml
1 kg = 1000 g
Then, you obtain the following results:
Brass:

Cooper:
That first one you have selected (3,-3) works in both equations so it's correct.
good job.
you can do this guess and test method with multiple choice answers. If it works in both equations it is the solution. Otherwise use substitution or elimination to combine the two into one equation in only one variable. Then you can solve for the one variable first and use it to solve for the other.
Answer:
299,792,458 m/s = speed of light
Explanation: