The loudness of a lawnmower is measured in decibels, modeled by the formula 90 = 10 log (StartFraction I Over I Subscript 0 Baseline EndFraction). What does 90 represent?

the initial loudness of the lawnmower
how loud the sound of the lawnmower is
the intensity of the sound of the lawnmower
the intensity of the sound of the lawnmower compared to the intensity of sound that is barely audible