Bernie: "Hello, Olli! You are right: Airplanes really do fly very high up in the sky - at about an altitude of 10,000 meters over the ground. Of course, there are reasons for this. Among others, the air gets thinner the higher up one goes. This means the air resistance is lower for the airplane, enabling it to fly faster, while at the same time using less fuel."
Lexi: "Furthermore, there are much fewer obstacles at this altitude. There are no mountains in the way and also the storms that occur in mountain regions are far away. So, as you see Olli: It is safer, less expensive and better for the environment to fly that high up!"