As an airplane approaches the airport it starts its descent

As an airplane approaches the airport, it starts its descent 50 miles away and takes 20 minutes to descend from an altitude of 30,000 feet. Assume that the airliners altitude A is a linear function of time t measured in minutes after it begins its descent. Find the slope of the linear function in feet per minute. -1500 1500 600 -600 None of the others

Solution

Since airlines altitude A is a linear function of time.

Airlines current altitude = 30,000 feet

final altitude = 0 feet                                  //    as it lands on the airport

Total change in distance = 0 - 30,000 = -30,000 feet

time taken = 20 mins

slope = distance / time                      //      slope = average rate of change in altitude

slope = -30000 / 20

slope = -1500 feet / min