distance/speed/wind problem

Question

a small plane cruises at 150mph in still air, and its rank has enough gas for 6 hours of flying.  if it takes off against a constant east wind of 50mph, how far can it fly in that direction and return safely?   the answer is 400 miles, but i cant seem to work out why.

Answer 1

Going into the wind, it's travelling at 150 - 50 = 100 mph. Conversely, it's travelling 150 + 50 = 200 mph coming back, or twice as fast. The distance is equal

 

Can you get it from here?