There are two stations 'A' and 'B'. A train from station 'A' with a speed of 60 km/hr moved towards station'B'. Simultaneously, a train from station B moves towards station 'A' with a speed of 40 km/hr. From station B trains are leaving at a fixed interval of 'n' minutes. The train from 'A' and first train from 'B' meets after half an hour. The train from A meets a total of 6 trains from B till it reaches station 'B'. What is the value of 'n' if last train met was just at station 'B'