To determine the period of a wave you need not utilize the value for the wave speed.
The formula for the period is T= 1/f
T stands for period/time while f is for frequency. Substitute the value for the frequency which is 60 Hz. That would give you:
T= 1/60 Hz
convert Hz to cycles per second to extract the unit of time (s).
60 Hz x 1/s/1 Hz= 60/s
To continue the computation:
T=1/60/s that will give you a T= 0.017 s or 17 ms.