Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s Speed of light = 3 × 108 m/s
Time taken by the laser beam to reach Moon = (1/2) x 2.56 = 1.28s
Radius of the lunar orbit
= Distance between the Earth and the Moon
= 1.28 × 3 × 108
= 3.84 × 108 m = 3.84 × 105 km