Alright, lets get started.
Ben left at 8:00 AM and Al left at 11:00 AM.
Suppose dispatcher retrieves data after t hrs when Al left SD.
We know the average speed of Al = 40 miles per hr
So, distance covered by Al = Time * speed
Distance covered by Al = 40 t
We know average speed of Ben = 20 miles per hr
As we know Ben left SD 3 hrs before, time taken by Ben will be 3 hrs higher than AL means (t+3)
So distance covered by Ben =
Total distance covered by both will be =
Total distance covered by both will be =
Total distance covered by both will be =
But as per given in question, total distance covered by both is 240 miles.
Hence making both equal,
Subtracting 60 from both sides
Dividing 60 in both sides
t = 3 hrs
It means it was 11:00 AM + 3 hrs means 2:00 PM when dispatcher retrieve data. : Answer
Hope it will help :)