The ratio of the speed of boats ‘A’ and ‘B’ in still water is 8:9, respectively. The speed of the current is 25% of the speed of boat ‘A’ in still water. If boat ‘A’ takes 8 hours to travel 640 km downstream, then find the time taken by boat ‘B’ to travel 168 km upstream and 880 km downstream. (Note: Both the boats are rowing in the same stream.)