distance=speed×time, so time=distance/speed=600/200=3 hours. If it takes 3 hrs without the wind for a one-way journey, it should take less time with a tailwind. If it still takes 3 hrs the wind speed is zero. With a headwind it would take more than 3 hours for a one-way journey. If x mph is the speed of the tailwind then the time for the one-way journey is 600/(200+x)<3 when x>0. Example: If the wind speed of a tailwind is 50mph, the time would be 600/250=2.4hrs (2hrs 24mins). If the wind speed is 100mph, the time is 600/300=2hrs. If the headwind speed is 50mph, the time would be 600/150=4hrs and 6hrs with a 100mph headwind.