Chapter 4.5, Problem 80PE

For Exercises 79-80, the formula $L=10\log \left(\frac{I}{I_0}\right)$

gives the loudness of sound L (in dB) based on the intensity of sound I (in W/m²). The value $I_0={10}^{-12}{\text{W/m}}^{\text{2}}$

is the minimal threshold for bearing for mid-frequency sounds. Hearing impairment is often measured according to the minimal sound level (in dB) detected by an individual for sounds at various frequencies. For one frequency, the table depicts the level of hearing impairment.

Category	Loudness (dB)
Mild	$26\le L\le 40$
Moderate	$41\le L\le 55$
Moderately Severe	$56\le L\le 70$
Severe	$71\le L\le 90$
Profound	$L>90$

Determine the range that represents the intensity of sound that can be heard by an individual with severe hearing impairment.