Final answer:
The time at the Prime Meridian is known as Greenwich Mean Time (GMT). Since the plane is flying over Russia at 90°E, which is 90 degrees away from the Prime Meridian, there is a time difference of 6 hours. Therefore, if it is 6pm in Russia, it would be 12pm (noon) at the Prime Meridian.
Step-by-step explanation:
The Prime Meridian is the line of longitude that passes through the Royal Observatory in Greenwich, England. It is located at 0 degrees longitude and divides the Earth into the Eastern and Western Hemispheres. The time at the Prime Meridian is known as Greenwich Mean Time (GMT).
In this case, the plane is flying over Russia at 90°E. Since the Prime Meridian is located at 0 degrees longitude, there is a time difference of 90 degrees between the plane's location and the Prime Meridian.
Each hour, the Earth rotates by 15 degrees, so the plane is 6 hours ahead of the Prime Meridian. Therefore, if it is 6pm in Russia, it would be 12pm (noon) at the Prime Meridian.