A plane directly above Denver, Colorado, (altitude 1650 meters) flies to Bismarck, North Dakota (altitude 550 meters). It travels at 750 km/hour at a constant height of 7000 meters above the line joining Denver and Bismarck. Bismarck is about 850 km in the direction 60° north of east from Denver. Find parametric equations describing the plane's motion. Assume the origin is at sea level beneath Denver, that the x-axis points east and the y-axis points north, and that the earth is flat. Measure distances in kilometers and time in hours. r(t) = ?