Velocity of sound in vacuum is .... $ms^{-1}$

When sound waves travel from air to water,which of the following remains constant?

At what temperature (in $^\circ C$) will the speed of sound in air be $3$ times its value at $0^\circ C$ (in $^\circ C$)?

$A$ person in front of a mountain is beating a drum at the rate of $40$ per minute and hears no distinct echo. If the person moves $90 \, m$ closer to the mountain,he has to beat the drum at $60$ per minute to not hear any distinct echo. The speed of sound is .............. $ms^{-1}$.

Explain which properties are necessary to understand the speed of mechanical waves.

The speed of sound in air: