Consider the Friis' transmission equation \(P_R=\dfrac{P_TG_TG_R\lambda^2}{(4\pi D)^2}\), where \(P_R\) and \(P_T\) are the received and the transmitted powers, respectively. \(G_T\) and \(G_R\) are the gain of transmitting and receiving antennas, respectively, \(D\) is the distance between the transmitting and receiving antennas, and \(\lambda\) is the wavelength in free space.
Given: \(G_T=G_R=1.0\), \(\lambda=0.30\text{ m}\) and \(P_T=+10\text{ dBm}\).
Choose the distance \((D)\), in km, from the following options at which the received power, \(P_R=-90\text{ dBm}\)?