Theory:

The distance travelled by a sound wave per unit time as it propagates through an elastic medium is known as the speed of sound.
 
Speed(v)=DistanceTime
 
If one wavelength (λ) represents the distance travelled by one wave, and one time period (\(T\)) represents the time taken for this propagation, then
 
Speed(v)=Onewavelength(λ)Onetimeperiod(T)
 
And, we know
 
T=1v
 
By applying this in speed formula, we get
 
v=nλ
 
Under the same physical conditions, the speed of sound in a given medium remains nearly constant for all frequencies.
 
Let us solve following example for better understanding.
 
Example:
 
A sound wave has a frequency of \(2\) \(kHz\) and a wavelength of \(15\) \(cm\). How much time will it take to travel \(1.5\) \(km\)?
  
Given data:
 
Frequency \(=\) \(2\) \(kHz\) \(=\) \(2000\) \(Hz\)
 
Wavelength \(=\) \(15\) \(cm\) \(=\) \(0.15\) \(m\)
 
Distance \(=\) \(1.5\) \(km\) \(=\) \(1500\) \(m\)
  
To find: Time period
 
Formula:Time=DistanceSpeed
 
We don't know the value of speed,
 
v=nλ
 
v=2000×0.15=300m/s
 
Now, apply in the value of speed in time formula
 
Time=1500300=5s
 
The sound will take \(5\) \(s\) to travel a distance of \(1.5\) \(km\).