Determine the minimum and maximum wavelengths of sound in water...

The relation between speed, frequency, and wavelength is given by $v = f \lambda$.

The minimum wavelength corresponds to the maximum frequency:

\lambda_\min = \dfrac{v}{f_\max}

\lambda_\min = \dfrac{1450}{20000} = 0.0725 \text{ m} = 7.25 \text{ cm}

The maximum wavelength corresponds to the minimum frequency:

\lambda_\max = \dfrac{v}{f_\min}

\lambda_\max = \dfrac{1450}{20} = 72.5 \text{ m}

The minimum and maximum wavelengths are $7.25 \text{ cm}$ and $72.5 \text{ m}$ respectively.