1. The problem statement, all variables and given/known data Mission control sends a brief wake-up call to astronauts in a far away spaceship. 2.4 seconds after the call is sent, Mission Control can hear the groans of the astronauts. How far away (at most) from Earth is the spaceship? 2. Relevant equations Have yet to find a suitable equation for this problem. 3. The attempt at a solution I do believe that this problem has to do with light properties and/or radio waves, but I'm unsure which one. I'm also wondering would the mediums (air and vacuum of space) that these waves travel through would severely affect the possible velocity of the waves? So far, I can assume that we need to know how fast these radio waves are traveling, since we are given the time only, and from there we can calculate the distance that the space shuttle is away. But I'm just lacking the other variables, so do I go online and apply real world data for this one? thank you!