1. The problem statement, all variables and given/known data A plane travels 3000 mi in 4 hours, when the wind is favorable the plane averages 900 mph. When the wind is unfavorable the wind averages 500 mph. During how many hours was the wind favorable. 2. Relevant equations 3. The attempt at a solution To me this looks like a simple equation. Let x stand for favorable wind 900x + 500y = 3000 y = (1/500)(3000-900x) the book is telling me the answer is 5/2 hours. plugging 5/2 gives me a y value that satisfies the equation, but I am wondering, wouldn't the equation be satisfied for all values of y, s.t. 0<x≤3 meaning the plane could have flew for 2 hours in favorable win, and 2.4 hours in unfavorable wind, and my answer would still be correct?