Final answer:
The plane descended at a rate of approximately 5 meters per second.
Step-by-step explanation:
To determine the speed at which the plane descended, we need to calculate the plane's average velocity in the downward direction. We can do this by dividing the change in elevation by the change in time. Looking at the graph, we can see that the plane's elevation decreases from 0 to -15 meters, which is a drop of 15 meters. The graph doesn't provide the time it took for the plane to descend, so we cannot determine the exact speed of descent. However, we can still answer the question by using the given options and comparing them to the magnitude of the slope of the graph.
Since the slope of the graph is negative, indicating a descent, we can estimate that the plane descended at a rate of approximately -15 meters per unit of time. Comparing this to the answer options, we can see that (b) 5 meters per second is the closest option to the negative slope of the graph. Therefore, the plane descended at a rate of approximately 5 meters per second.