Compressional waves can travel through all states of matter.
C Occupational Safety and Health Administration
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To solve this problem we will apply the concepts related to pressure, depending on the product between the density of the fluid, the gravity and the depth / height at which it is located.
For mercury, density, gravity and height are defined as
For the air the defined properties would be
We have for equilibrium that
Replacing,
Rearranging to find
Therefore the elevation of the mountain top is 9400ft