Explanation:

- Travel time upstream: 3 hours 12 minutes = 3.2 hours.

- Distance upstream: 40 km.

- Speed of boat upstream = Distance/Time = 40 km / 3.2 hr = 12.5 km/hr.

- Current speed = 3 km/hr.

- Speed of boat in still water = 12.5 km/hr + 3 km/hr = 15.5 km/hr.

- Speed increase: 15.5 km/hr * 1.2 = 18.6 km/hr (new boat speed in still water).

- Speed downstream = 18.6 km/hr + 3 km/hr = 21.6 km/hr.

- Time for 54 km downstream = Distance/Speed = 54 km / 21.6 km/hr ˜ 2.5 hours.

Options:

1. 1 hour 30 min

2. 1 hour 20 min

3. 2 hour 30 min

4. 3 hour 15 min

5. 2 hour

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