Electromagnetic Waves Part 1

A radar sends an electromagnetic signal of electric field (E0)=2.25V∕m and magnetic field (B0)=1.5×10−8T which strikes a target on line of sight at a distance of 3‌km 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 t=0 from radar, then after how much time echo will reach to the radar?