One layer of earth's atmosphere is called the stratosphere. at one point above earth's surface, the stratosphere extends from an altitude of 16 kilometers to an altitude of 50 kilometers. the compound inequality that represents the stratosphere above earth's surface using the variable k is

At this point of the Earth's surface, the Stratosphere layer is at most at 50 km, and at least at 16 km altitude.

If y represents a height which is in the Stratosphere layer, then we know that y is at least 16 km, which is represented by  , 

and y is at most 50 km, which is represented by .

Combining these 2 inequalities we have:

, where y is in km