Two trains 'A' and 'B' are at station 'X' and station 'Y' respectively. Train 'A' starts from station 'X' towards station 'Y' and train 'B' starts from station 'Y' towards station 'X'. The distance between station 'X' and station 'Y' is 600 km. If the speed of train 'A' is constant at 'a' km/hr and that of train 'B' is constant at (a + 20) km/hr and both trains make continuous journey between two stations then the total distance covered by train 'B' till their third meeting will be 1800 km. Find the distance between both the trains after 5 hours?