I can really explain it well, but I have the answers.
It will take a total of 15 minutes for the plane to land.
When 5 minutes have passed the plane will be at 20,000 feet.
Given the planes altitude from 30,000 - 2,000 per/min every minute the plane goes down 2,000 (30,000 {1 min passes} 28,000 now. so on and so forth)
