Answer
$I = 2.0\times 10^{-5}~W/m^2$
Work Step by Step
The power spreads in all directions from the antenna. We can find the intensity at a point 10 kilometers away as:
$I = \frac{P}{A}$
$I = \frac{P}{4\pi~R^2}$
$I = \frac{25,000~W}{(4\pi)(10,000~m)^2}$
$I = 2.0\times 10^{-5}~W/m^2$
