Answer
35 kW
Work Step by Step
The average intensity is given by equation 22–8.
$$\overline{I}=\frac{1}{2}\epsilon_ocE_o^2$$
$$=\frac{1}{2}(8.85\times10^{-12}C^2/(N \cdot m^2)) (3.00\times10^8m/s)(0.12V/m)^2$$
$$=1.9116\times10^{-5}\frac{W}{m^2}$$
Assume that the radio station radiates uniformly. Imagine a sphere, centered at the station, whose radius is 12 km. The $1.9116\times10^{-5}\frac{W}{m^2}$ is the average intensity. This is equal to the radio station’s total power, distributed over the surface of the imaginary sphere.
$$I=\frac{P}{A}$$
$$P=IA=(1.9116\times10^{-5}\frac{W}{m^2})4\pi(12\times10^{3}m)^2=35kW$$