Question 1012409
Call its rate in still air, r.
Call the rate of the wind, w.
In general rate times times equal distance.
We can then write and solve this system:
4(r + w) = 4200
5(r - w) = 4200
Let's divide the first by 4 and the second by 5 and get
r + w = 1050
r - w = 840
Now add equations and get
2r = 1890
r = 945 mph
Thus w = 105 mph