A. Elephant makes call at 20Hz. Elephant calls in air. speed of sound in air = 343 m/s
wavelength = speed/frequency = 343/20 = 17.15m
B. Bluewhale stays in water. Speed of sound in water is more than speed of sound in air. When blue whale calls at 20Hz, the wavelength of the call is 75m which is much higher than the wavelength of wave when it is called by elephant.
