The frequency of a wave is given by:
[tex]f=\frac{v}{\lambda}[/tex]
Where v is the speed of the wave and lambda is the wavelenght. In this case the speed is 345 and the wavelenght is 0.85 meters; plugging the values given we have:
[tex]\begin{gathered} f=\frac{345}{0.8} \\ f=431.25 \end{gathered}[/tex]
Therefore the frequency of the wave is 431.25 Hz
