a plan can fly 1200 miles with the wind in 3 hours, while it takes the same plan 4 hours to fly the same distance against the wind. Find the speed of the plan in still air, and the speed of the wind.
If the plane's speed is p and the wind's speed is w, then
1200/(p+w) = 3
1200/(p-w) = 4
rearrange to get
3p+3w = 1200
4p-4w = 1200
or,
p+w = 400
p-w = 300
Now just solve for p and w.