The mesosphere is the layer of Earth's atmosphere between 50 kilometers and 85 kilometers above
Earth's surface. At a distance of 50 kilometers from
Earth's surface, the temperature in the mesosphere is
-5° Celsius, and at a distance of 80 kilometers from
Earth's surface, the temperature in the mesosphere is
- 80° Celsius. For every additional 10 kilometers
from Earth's surface, the temperature in the
mesosphere decreases by k Celsius, where k is a
constant. What is the value of k?