The intensity of a wave is given by the ratio between the power P of the source and the surface A over which it is calculated:
[tex]I= \frac{P}{A} [/tex]
For the sound wave in this problem, the power is P=0.30 W. Since a sound wave propagates radially, the area that we should use is the surface of of a sphere with radius r=1.6 m:
[tex]A=4 \pi r^2 = 4 \pi (1.6 m)^2 =32.15 m^2[/tex]
Therefore, the intensity is
[tex]I= \frac{P}{A}= \frac{0.30 W}{32.15 m^2}=9.33 \cdot 10^{-3} W/m^2 [/tex]
