The period of a wave can be calculate according T = 1 / f
where T is wave period and f is frequency,
then in our problem we have a wave of 100 Hz so:
T = 1 / 100 = 0.01 seconds
The wave have a period of 0.01 seconds.
Optinaly we could also calculate the speed: V=wavelenght/period= 2/0.01= 200 m/s
