Correct answer:
By the way, you should've written 260 mph, and not 260 miles.
IGNORE the RUBBISH/NONSENSE the other person posted.
We are given: Average speed of 280 mph from X to Y. Average speed of 260 mph from Y to X. Time for the flight (Y --> X) is 12 minutes longer than that for (x --> Y). Let t be the time for the flight (Y --> X) (which is under the question). Then 280*(t-1/6) = 260*t. (1) This equation says that the distance was the same for both flights. Notice that= of an hour = 10 minutes. From (1) you have 280*t - 280/6 = 260*t ====> 280*t - 260t = -280/6 ====> 20*t = 280/6 ====> t = = = = hours. Answer. The flight from Y to X was hours.