The diagram is missing; however, we know that the intensity of a sound wave is inversely proportional to the square of the distance from the source:
[tex]I(r)= \frac{1}{r^2} [/tex]
where I is the intensity and r is the distance from the source.
We can assume for instance that the initial distance from the source is r=1 m, so that we put
[tex]I= \frac{1}{r^2}= \frac{1}{(1)^2}=1 [/tex]
The intensity at r=3 m will be
[tex]I= \frac{1}{r^2}= \frac{1}{(3)^2}= \frac{1}{9} [/tex]
Therefore, the sound intensity has decreased by a factor [tex]1/9[/tex].
