Practice: Calculating density, mass, and volume!

1)  If the density of an object is 2.1g/mL, and it extends about 7.5cm with a height of 5cm, and it is 4mm wide,what is its mass?

2)  If the mass of an object is 15g, and its density is 3.5g/mL, what is its volume?

3)  In a graduated cylinder, there are 14mL of water, if a 16g marble was dropped in the cylinder, and the water rose to a level of 23mL, what is its density?