Now ... The question gives you the speed and the frequency, but they're stated in unusual ways, with complicated numbers.
Frequency: How many each second ? The thing that's making the waves is vibrating 47 times in 26.9 seconds. Frequency = (47) / (46.9 s) = 1.747... per second. (1.747... Hz)
Speed: How far a point on a wave travels in 1 second. The crest of one wave travels 4.16 meters in 13.7 seconds. Speed = (4.16 m / 13.7 sec) = 0.304... m/s
Wavelength = (speed) / (frequency)
Wavelength = (0.304 m/s) / (1.747 Hz) = 0.174 meter per second
