lift / drag ratio question
My brain is tired. Here is a question that I am not getting correct:
A glider is flying from A to C. With a normal L/D ratio of 20:1 and a constant airspeed of 40 MPH, what minimum altitude AGL is needed at B to arrive over C at 800 feet AGL with no sinking air?
The distance from A to B is 15 miles and from B to C is 20 miles. We have a tailwind of 20 mph.
The answer is listed as 4320 feet.
Thx. I'm sure it is simple, but I keep getting a different answer!