The question was as follows
TAS - 197 kts
Course - 240
Wind - 180/30
Descending from FL 200 to FL 40
Horizontal Distance travelled - 39 NMs
What is the ROD?
As per this question, you will have to find the angle. Vertical distance lost is 16,000 feet and horizontal distance travelled is 39 nm (or 237,120 feet).
Now find tan Ө .
tan Ө = perpendicular/base ---> tan Ө = 16000/237120
You get tan Ө = 0.06747
Therefore, Ө = 3.86 degrees
Then apply that to the formula,
Rate of descent = Groundspeed x Glide slope angle x 100/60
You will get the
ROD as 1158 feet per minute.
(I hope this is correct. If not, kindly correct me but please be polite)