A wave oscillates 5.0 times a second and has a speed of 4.0 m/s.
A. The frequency of any wave is the number of times it oscillates in one second. That's given in the question.
Frequency = 5.0 Hertz.
B. The period of any wave is the reciprocal of its frequency.
Period = (1 / 5.0 Hz)
Period = 0.2 second .
C. The wavelength of any wave is (speed / frequency).
Both of these numbers are given in the question.
Wavelength = (4.0 m/s) / (5.0 Hz) .
Wavelength = 0.8 meter .