At maximum speed an airplane travels 2100 miles against the

At maximum speed, an airplane travels 2100 miles against the wind in 6 hours. Flying with the wind, the plane can travel the same distance in 4 hours. What is the speed of the plane with no wind?

2,100/6=350 mph against the wind
2,100/4=525 mph with the wind
(525-350)/2=175/2=87.5 mph is the speed of the wind
350+87.5=437.5 is the speed of the airplain in still air.
525-87.5=437.5 ditto.