A radar sends an electromagnetic signal of electric field ( E_o )=2.25 V / m and magnetic field ( B_o )=1.5 × 10^-8 T which strikes a target on line…

A radar sends an electromagnetic signal of electric field $\displaystyle \left(\mathrm{E}_{\mathrm{o}}\right)=2.25 \mathrm{~V} / \mathrm{m}$ and magnetic field $\displaystyle \left(\mathrm{B}_{\mathrm{o}}\right)=1.5 \times 10^{-8} \mathrm{~T}$ which strikes a target on line of sight at a distance of $\displaystyle 3$ km in a medium. After that, a part of signal (echo) reflects back towards the radar with same velocity and by same path. If the signal was transmitted at time $\displaystyle \mathrm{t}=0$ from radar, then after how much time echo will reach to the radar?