Density problem solving?

Question

please help me with this. I don't get it.

1. What is the density of a piece of cement that has a mass of 8.76 g and a volume of 3.07 mL?

it would be nice if you could explain how you got the answer because i have to solve other problems like this. I already understand that density=mass/volume..

Answer 1

a. A recycling center has a 125,000 cm3 box filled with one type of plastic. When empty, the box

had a mass of 755 grams. The full box has a mass of 120.8 kg (120,800 g). What is the density

of the plastic? What type of plastic is in the box?

Answer 2

the density of a lquid is 3.0g/ml.
the mass  in kg.of 40ml
the volume in liters of 10grams

Answer 3

wew