The distance between the first and third crest of an ocean wave is 24 meters. what is the wavelength of the ocean wave? a. 6 meters b. 8 meters c. 12 meters d. 24 meters

The answer is C. 12 meters.

The distance between the crests of an ocean is 1 wavelength. Between the first and the second crest, the distance is 1 wavelength while between the first and the third crest the difference is 2 wavelengths.
If 24 meters are 2 wavelengths, how many meters are 1 wavelength:
24m : 2w = x : 1w
⇒
⇒ x = 12 meters.