Read the passage below and solve the questions based on it.
Three persons A, B and C start running simultaneously on three different concentric circular tracks from three collinear points P, Q and R respectively which are collinear with the centre O and are on the same side of the centre as shown. The speeds of A, B and C are 5 m/s, 9 m/s and 8 m/s respectively. The lengths of the tracks on which A, B and C are running are 400 m, 600 m and 800 m respectively.
If A runs in the clock wise direction and C in the anti-clockwise direction, after how much time will the positions of A and C be collinear with the centre, (and on the same side), for the fourth time after they start?