Explanation:

Let’s break it down step by step:

- The boat covers 32 km downstream in 2 hours, so its downstream speed = 32/2 = 16 km/h.

- Boat speed in still water is 12 km/h.

- Let’s say river speed = x km/h.

- Downstream speed = (boat speed + river speed) ? 16 = 12 + x, so x = 4 km/h.

- Upstream speed = (boat speed - river speed) ? 12 - 4 = 8 km/h.

Now, to cover 32 km upstream at 8 km/h:

- Time = distance/speed = 32/8 = 4 hours.

Let’s look at the options:

1. 6 hours (nope)

2. 3 hours (no)

3. 2 hours (no)

4. 4 hours (yes)

5. None (not needed)

Option 4, 4 hours, is correct.