Physics
posted by Pete .
For a certain transverse wave, the distance between two successive crests is 1.89 m, and 5 crests pass a given point along the direction of travel every 12.84 s. Calculate the wave speed.

The information you have been given allows you to calculate the frequency and the wavelength. In fact, they have told you what the wavelength is already.
The period is P = 12.85/5 = 2.57 s and the frequency is 1/P = ___ s^1.
The product of wavelength and frequency is the wave speed.
That should enable you to do the calculation.