Answer:
Water
Explanation:
The speed of light in water is about 230 million m/s.
Explanation:
Below is an attachment containing the solution.
To find the speed you multiply the wavelength and the frequency together.
wavelength = 8mm =

m = 0.008 m
frequency = 14 Hz
speed = 0.008m * 14 Hz = 0.112 m/s
You measure the distance between crest and crest or trough and trough