If you are going 50km/h for 4 hours then you travel a total of 200km so now you multiply 60 by 3 to get a total of 180km then subtract 180km from 200km to see what is missing then you get 20km and since you are going 60km/h and 20km are missing every km is a minute long so it would be 3 hours and 20 minutes.
