Recall your d = rt, distance = rate * time.
as the plane goes against the wind, the plane is not really flying at "x" mph, but is really going slower, at " x - y ", because the wind is subtracting speed from it.
likewise, when the plane is going with the wind, is not really going at "x" mph, but at " x + y ", is going faster due to the wind, thus
as the plane goes against the wind, the plane is not really flying at "x" mph, but is really going slower, at " x - y ", because the wind is subtracting speed from it.
likewise, when the plane is going with the wind, is not really going at "x" mph, but at " x + y ", is going faster due to the wind, thus