I didn’t want to include any part of my attempt at the question in the first post because I wanted to see someone else’s working out from start to finish but I will on this occasion to get the ball rolling and show that I have attempted this question.

36,000*2=72,000

Time = distance/speed

72,000/300,000

=0.24 of a second, 120 milliseconds each way

Feel free to continue this question where I have left off or correct anything I have done above because I am not 100% sure on anything about this question.