An airplane flying 1600 km covers the first 400 km at a speed of 200 km/hr, the second 400 km at a speed of 400 km/hr, and the third 800 km at a speed of 800 km/hr. Find the average speed of the airplane.
1
580 km/hr
2
900 km/hr
3
850 km/hr
4
400 km/hr