Ultrasonic waves of frequency 4.5 MHz are used to

Ultrasonic waves of frequency $4.5 \mathrm{MHz}$ are used to detect tumour in soft tissue. The speed of sound in tissue is $1.5 \mathrm{~km} \mathrm{~s}^{-1}$ and that in air is $340 \mathrm{~m} \mathrm{~s}^{-1}$. Find the wavelength of this ultrasonic wave in air and in tissue.