"A 35,000 kg plane is flying East at a cruising altitude of 27,000 ft. The pilot engages the auto-pilot feature allowing the plane to fly unassisted at its current altitude with a constant speed of 270 m/s. After 1 hour and 41 minutes the auto-pilot is disengaged as the plane begins its initial descent to the airport. Calculate how many kilometers the plane flies while on auto-pilot?" I figured that you'd simply multiply speed by time, but that isn't the case apparently.

The answer to the above question is 1640 km, but how would one come to that answer?