Explanation:

- The rower takes 12 hours to go 144 km upstream.

- So, upstream speed = 144 km / 12 hours = 12 km/h.

- The rower takes 9 hours to go 144 km downstream.

- So, downstream speed = 144 km / 9 hours = 16 km/h.

- Let the speed of the rower in still water be "b" km/h and speed of the stream be "s" km/h.

- Upstream speed: b - s = 12 km/h.

- Downstream speed: b + s = 16 km/h.

- Adding both equations:

- 2b = 28

- b = 14 km/h.

- Subtracting the first equation from the second:

- 2s = 4

- s = 2 km/h.

- Hence, the speed of the stream is 2 km/h.

Option:4, 2 km/h is the correct answer.

.