$102 headphones, 7.5% tax

You are correct the tax would be that

Step-by-step explanation:

0.5 g/mL float

1.0 g/mL float

2.0 g/mLsink

Explanation:

Those objects will float whose density is less or equal to water density due to lower mass while those object will sink whose density is greater than water because the mass of the object is greater than water. So the density of the object i. e. 0.5 g/mL and 1.0 g/mL will float in the liquid because its density is lower than water which is 1 g/mL while the density of an object i. e. 2.0 g/mL is denser than water so it will sink.