Two planes are flying away from each other in opposite directions each other in opposite directions. One plane flies 800 kilometers per hour, and the other plane flies 840 kilometers per hour. How much farther apart are the planes after 1 hour?
After 1 hour, the first plane will have traveled 800 km/hr * 1 hr = <<800*1=800>>800 kilometers.
After 1 hour, the second plane will have traveled 840 km/hr * 1 hr = <<840*1=840>>840 kilometers.
The two planes will be 800 km + 840 km = <<800+840=1640>>1640 kilometers farther apart. Answer: \boxed{1640}.