Explanation:

- The boat takes 4 hours to cover distance D km upstream.

- The boat takes 3 hours to cover distance D - 2 km downstream.

- The speed of the stream is 2 km/hr.

Let's calculate:

- Upstream speed = boat speed - stream speed.

- Downstream speed = boat speed + stream speed.

From the upstream trip:

$$ D = (boat\_speed - 2) \times 4 $$

From the downstream trip:

$$ D - 2 = (boat\_speed + 2) \times 3 $$

Solve these two equations to find the boat's speed, then determine the distance covered upstream in 3 hours:

- Let x be the boat speed.

- Equation 1: \( D = (x - 2) \times 4 \) (1)

- Equation 2: \( D - 2 = (x + 2) \times 3 \) (2)

From equation 1:

$$ x - 2 = \frac{D}{4} $$

So, \( D = 4(x - 2) \).

Substituting D from equation 1 in equation 2:

$$ 4(x - 2) - 2 = 3(x + 2) $$

Expand and solve:

$$ 4x - 8 - 2 = 3x + 6 $$

$$ 4x - 10 = 3x + 6 $$

$$ x = 16 $$

Speed of the boat = 16 km/hr.

Now, upstream speed = 16 - 2 = 14 km/hr.

Distance covered upstream in 3 hours:

$$ 3 \times 14 = 42 $$

So, the correct option is: Option 1 - 42 km

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