To make sure that we have enough resourses to sustain ourselves. You see, if we use up, say, all water on earth, then obviously we won't have any more and we'll die.
The 120 decibel sound has more amplitude than the 100 decibel sound.
In Physics, the relation between amplitude and intensity is that the intensity of the wave is directly proportional to the square of its amplitude.
The answer is 8.
Hope I helped.
