The question reads:

"A glider is moving with a velocity

relative to the air and is blown by the wind which has velocity relative to the earth of

. Find the velocity of the glider relative to the earth."

My argument goes that as the velocity of the wind relative to the earth increases, and the velocity of the glider relative to the air, increase, so does the velocity of the glider relative to earth. So if we let

represent the velocity of the glider relative to the earth,

.

Therefore, in this case the velocity of the glider relative to the earth,

However, the answer booklet has the expression for

as follows:

giving

which I suppose must be the right answer. Could somebody explain this result to me? Thank you.