Answer:
It descends 3 km.
Explanation:
The rate of change is the slope. The formula for slope is

Using the first two points, (0, 12) and (2, 10), we have
m = (10-12)/(2-0) = -2/2 = -1
This means the plane descends 1 km per minute. This means in 3 minutes' time, the plane descends 3 km.