The attenuation (intensity loss) of ultrasound in tissue is approximately 0.3 dB per MHz per cm of depth. (E.g., a 3 MHz signal travelling during 2 cm of tissue has its initial intensity reduced by 0.3×3×2 = ?1.8 dB.) About how deep into the tissue 10.5 MHz transducer probes before the intensity can is reduced to one eighth of its initial value? Suppose a decrease of 3 dB corresponds to a halving of intensity.
Give your answer in centimetres to one important figure. (Don't enter unit.) Note: Though a formula can be utilized, the required accuracy does not demand it.