As we know that intensity of sound is defined as power received per unit area
so here the power of source is given as
[tex]P = 39 W[/tex]
distance of microphone is given as
[tex]d = 60 m[/tex]
now if loudspeaker is considered as spherical source then we will have
[tex]Intensity = \frac{power}{area}[/tex]
[tex]Intensity = \frac{39}{4\pi r^2[/tex]
here
r = d = 60 m
[tex]Intensity = \frac{39}{4\pi (60^2)}[/tex]
[tex]Intensity = 0.86 \times 10^{-3} W/m^2[/tex]