Assuming that sound waves travel along a straight line at a constant speed of 346 m/s, we can find the time needed for the sound to travel the distance of 1.9 m between the astronauts, just applying the definition of average velocity, as follows:
The electromagnetic waves travel in free space at the same speed of light in vacuum ( since light is a electromagnetic wave indeed), i.e., 3*10⁸ m/s.
Applying the same formula than in (1) we can solve for the distance d, as follows:
