The frequency of the waves is 107.14 Hz.
To find the frequency of the waves, we need to divide the wave speed by the wavelength.
The wave speed is given as 54 km/hr, which is equal to 54,000 m/hr or 15 m/s.
The wavelength is given as 140 mm, which is equal to 0.14 m. So, the frequency can be calculated as:
Frequency = Wave Speed / Wavelength
Frequency = 15 m/s / 0.14 m
Frequency = 107.14 Hz
Therefore, the frequency of the waves is 107.14 Hz.