The answer to your question depends upon your reason for asking it.
This question also appears in the Tech Log Forum. As stated by BOAC in that forum by, in the real-world the solution of this type of problem is quite complex.
If you are preparing to take ATPL exams the question becomes a bit easier. Complex questions of this type are rare in the JAR ATPL exams but quite common in some others such as the Indian DGCA ATPL and CPL exams.
The questions include the distances between the various locations plus the wind speed/direction and the TAS or the ground speed for each leg of the flight. With this information you can apply the formula in the usual way using the appropriate speeds and distances.
Pass rates for JAR ATPL exams are usual better than 90%. Pass rates for the Indian DGCA exams are usually closer to 5%.