The frequency of a wave is given by:
[tex] f=\frac{N}{t} [/tex]
where
N is the number of complete cycles of the wave
t is the time taken
For the wave in this problem, we have 57 oscillations in 3.0 seconds, therefore N=57 and t=3.0 s. Substituting these numbers into the equation, we find
[tex] f=\frac{N}{t}=\frac{57}{3.0 s}=19 Hz [/tex]
