Sound waves traveling through liquids tend to move faster than sound waves traveling through and, in general, sound waves move the fastest through

gas

solids

Explanation:

The speed of sound depends upon the properties of the medium it is passing through

sound waves travel

Why fastest in solids?

Sound is a spherical longitudinal wave. It propagates through compressions and refractions of particles

In solids, the particles are tightly packed and the space of separation between them is less.So, the time taken for a particle to collide with another is comparatively less because they have to travel a relatively short distance with their velocity.

Therefore, there are more collisions per second and particles move faster causing the wave to propagate faster

But in gases sound takes a larger time to propagate because the molecules of gases are far apart from each other

d.7.5cm is your answer