What is the Algebra formula and solution to: A small plane travels 200 mph with the wind and 120 mph against it. What is the speed of the wind and the speed of the plane in still air?

If p is the speed of the plane, and w is the speed of the wind, you have
  p + w = 200
  p - w = 120

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You can find p by adding these equations
  2p = 200 + 120 = 320
  p = 160
From either equation,
  w = 40
The speed of the wind is 40 mph, the speed of the plane in still air is 160 mph.