## Precalculus (6th Edition) Blitzer

$x+y$, $x-y$
When the plane travels with the wind, the resulting velocity will be the sum of the two individual velocities $x+y$ of the plane and the wind. On the other hand, when the plane travels against the wind, the resulting velocity will be the difference of the two individual velocities $x-y$ of the plane and the wind. Thus, the answers are $x+y$ and $x-y$.