Explanation:

- The speed of the boat in still water is denoted as 'b' km/hr and the speed of the current is 'c' km/hr.

- Equation 1: For the 300 km upstream journey in 10 hours, the speed upstream is calculated as \( (b - c) \). So \( b - c = 30 \) km/hr.

- Equation 2: For the 60 km upstream and 120 km downstream with equal time, let 't' be the time. Thus, \( \frac{60}{b - c} = \frac{120}{b + c} \).

- Use Equation 1: \( b - c = 30 \). Set it into Equation 2 and solve to get \( b + c = 60 \).

- Solve the system of equations:

- \( b - c = 30 \)

- \( b + c = 60 \)

- Adding them gives \( 2b = 90 \) leading to \( b = 45 \) km/hr.

- ?? Correct Answer: Option 3, 45 km/hr.

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