P cycles at a speed of 4 m s for the first 8 seconds 5 m s for the next 8 seconds 6 m s for the next...........

Explanation:

Distance covered by P in 8 sec = 4 * 8 = 32 m
Distance covered by P in 16 sec = 32 + 5 * 8 = 72 m
Distance covered by P in 24 sec = 72 + 6 * 8 = 120 m
Distance covered by P in 32 sec = 120 + 7 * 8 = 176 m
Distance covered by P in 40 sec = 176 + 8 * 8 = 240 m
Distance covered by P in 48 sec = 240 + 9 * 8 = 312 m
Distance covered by P in 56 sec = 312 + 10 * 8 = 392 m
Total distance in 56 sec = 392m
To cover balance 436 - 392 = 44 m with speed = 11 m/sec, time taken = 44/11 = 4 sec
So P would finish 436 m in 56 + 4 = 60 seconds.
In 60 seconds, Q cycles 60 * 6.5 = 390 m or B should have a 436 - 390 = 46m lead to result in a dead heat.