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 = ![20 (t + 3)](https://tex.z-dn.net/?f=%2020%20%28t%20%2B%203%29%20)
Total distance covered by both will be = ![40 t + 20 (t+3)](https://tex.z-dn.net/?f=%2040%20t%20%2B%2020%20%28t%2B3%29%20)
Total distance covered by both will be = ![40 t + 20 t + 60](https://tex.z-dn.net/?f=%2040%20t%20%2B%2020%20t%20%2B%2060%20)
Total distance covered by both will be = ![60 t + 60](https://tex.z-dn.net/?f=%2060%20t%20%2B%2060%20)
But as per given in question, total distance covered by both is 240 miles.
Hence making both equal,
![60 t + 60 = 240](https://tex.z-dn.net/?f=%2060%20t%20%2B%2060%20%3D%20240%20)
Subtracting 60 from both sides
![60 t + 60 - 60 = 240 - 60](https://tex.z-dn.net/?f=%2060%20t%20%2B%2060%20-%2060%20%3D%20240%20-%2060%20)
![60 t = 180](https://tex.z-dn.net/?f=%2060%20t%20%3D%20180%20)
Dividing 60 in both sides
![\frac{60 t }{60} = \frac{180}{60}](https://tex.z-dn.net/?f=%20%5Cfrac%7B60%20t%20%7D%7B60%7D%20%20%3D%20%5Cfrac%7B180%7D%7B60%7D%20%20)
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 :)