Wave Speed

Speed is defined as distance over time.
When it comes to waves, the distance is wavelength and the time is period.
Hence, wave speed = wavelegth / period

Since period is the inverse of frequency, the wave speed formula can be written as follows:
wave speed = frequency × wavelegth ⇒ v = f × λ

This formula holds for all kinds of waves including water waves, sound waves, light waves, etc.