Answer
$I = 1.5\times 10^{-17}~W/m^2$
Work Step by Step
We can find the intensity received by the aircraft:
$I = \frac{P}{A}$
$I = \frac{P}{2\pi~R^2}$
$I = \frac{1.8\times 10^5~W}{(2\pi)~(9.0\times 10^4~m)^2}$
$I = 3.54\times 10^{-6}~W/m^2$
We can find the power reflected by the aircraft:
$P = I~A$
$P = (3.54\times 10^{-6}~W/m^2)(0.22~m^2)$
$P = 7.8\times 10^{-7}~W$
We can find the intensity at the radar site:
$I = \frac{P}{A}$
$I = \frac{P}{2\pi~R^2}$
$I = \frac{7.8\times 10^{-7}~W}{(2\pi)~(9.0\times 10^4~m)^2}$
$I = 1.5\times 10^{-17}~W/m^2$
