What is the mass of a marble cylinder with a diameter of .42m and a length of 1.25m?
Mass is volume times density.
I am sure you already know that the volume of a cylinder is
V = (pi/4) x (diameter)^2 x (length)
Marble is not a pure chemical compound, and can have a range of densities. You should look it up. I found one reference that says the density varies between 2.55 and 2.7 g/cm^3