The sound intensity is the ratio between the power of the wave and the surface:
[tex]I= \frac{P}{A} [/tex]
where
I is the intensity
P is the power
A is the area
In our problem, the sound intensity is [tex]I=2.13 \cdot 10^{-6} W/m^2[/tex], and the surface area of the ear is [tex]A=1.92 \cdot 10^{-3} m^2[/tex], so if we re-arrange the previous equation and we use these data we can find the sound power:
[tex]P=IA=(2.13 \cdot 10^{-6} W/m^2)(1.92 \cdot 10^{-3} m^2)=4.09 \cdot 10^{-9} W[/tex]
