The loudness level of a sound can be expressed by comparing the sound's intensity to the intensity of a sound barely audible to the human ear. The formula D - 10 ( log I - log In ) describes the loudness level of a sound, D, in decibels, where I is the intensity of the sound, in watts per meter", and In is the intensity of a sound barely audible to the human ear. Use this information to answer parts (a) and (b) below. a. Express the formula so that the expression in parentheses is written as a single logarithm