1. Suppose that during its flight, the elevation e (in feet) of a certain airplane and its timet in minutes since takeoff, are related by a linear equation. Consider the graph of this
equation, with time represented on the horizontal axis and elevation on the vertical
axis. For each situation, decide if the slope is positive, zero, or negative.
a. The plane is cruising at an altitude of 37,000 feet above sea level.
b. The plane is descending at rate of 1000 feet per minute.
c. The plane is ascending at a rate of 2000 feet per minute.