The basic relationship between frequency, wavelength and speed of a wave is given by: [tex]f= \frac{v}{\lambda} [/tex] where f is the frequency v is the wave speed [tex]\lambda[/tex] is the wavelength
The ultrasound wave in our problem has wavelength of [tex]\lambda = 0.19 mm = 0.19 \cdot 10^{-3}m[/tex] and speed of [tex]v=1.5 km/s = 1.5 \cdot 10^3 m/s[/tex] So its frequency is [tex]f= \frac{v}{\lambda}= \frac{1.5 \cdot 10^3 m/s}{0.19 \cdot 10^{-3} m}=7.89 \cdot 10^6 Hz [/tex]
