For research purposes a sonic buoy is tethered to the ocean floor and emits an infrasonic pulse of sound. The period of this sound is 68.4 ms. Determine the wavelength of the sound.
Let p denote the time of one period. Then
$\displaystyle f = \frac1p$ . Plug in the value of p and you'll get
$\displaystyle f = 14.62 \ \frac1s$
I take the value of the sound speed in water from my previous post. From
$\displaystyle f \cdot l = 1485\ \frac ms~\implies~ 14.62 \ \frac1s \cdot l = 1485\ \frac ms$ you can calculate l.
(For confirmation only: 101.6 m)