What is the air temperature outside the plane if it flies at an altitude of 9 km, and at the earth’s

What is the air temperature outside the plane if it flies at an altitude of 9 km, and at the earth’s surface the temperature is + 24 ° C °

It is known that the air temperature decreases with altitude: for every kilometer of altitude by six degrees Celsius. If the air temperature at the surface of the earth is plus twenty-four degrees, then at an altitude of nine kilometers it will be equal to minus thirty degrees. This is the difference between the temperature at the surface and the temperature at an altitude of nine kilometers.