ANSWER: 4.0
Step-by-step explanation:
34.0 - 30.0 = 4.0
When you subtract the volume of the water and sample you are given the mass of the object. For example, if you weighed an apple in a container at 15g and then you massed the apple at a roughly 8g.
15 - 8 = 7
So the container was 7g