Flight Noi Bai International Airport departs from Hanoi Noi Bai International Airport at 12:15 and arrives at Seoul Incheon International Airport at 18:50.
The flighttime is about 4h 35m. The distance travelled ("as the bird flies"): 2409 Km. So the average speed is roughly 526 Km.
There is an 2 hour time difference between Hanoi and Seoul