The mesosphere is the layer of the Earth's atmosphere between 50 kilometers and 85 kilometers above the earth's surface. At the distance of 50 kilometers from the earth's surface , the temperature in the mesosphere is -5° Celsius, and at a distance from 80 kilometers from the 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?