Let's denote the distance downstream as $3x$ kilometers and the distance upstream as $x$ kilometers.

We are given:

• Downstream speed = 15 km/h
• Upstream speed = 5 km/h
• Total time = 14 hours

To solve this, we'll use the formula for time:

$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$

Time taken for downstream journey:

$\text{Time}_{\text{downstream}} = \frac{3x}{15} = \frac{x}{5}$

Time taken for upstream journey:

$\text{Time}_{\text{upstream}} = \frac{x}{5}$

Total time:

The total time for both journeys is 14 hours, so:

$\frac{x}{5} + \frac{x}{5} = 14$

Simplifying the equation:

$\frac{2x}{5} = 14$

Multiply both sides by 5:

$2x = 70$

Now, divide by 2:

$x = 35$

The value of $x + 10$ is:

$x + 10 = 35 + 10 = 45$

It appears there is a mistake in the given options since the correct answer is 45, but none of the choices reflect this value. Could there be a typo in the problem or options?

Let me know if you want further clarification or any other help! Here are some related questions you might like:

1. How does the boat's downstream and upstream speed affect the time taken for a journey?
2. How would the total time change if the boat's speeds were different?
3. How do you calculate time in motion problems like this one?
4. What happens if the distances traveled downstream and upstream are the same?
5. How can we solve more complex boat motion problems with different speeds in both directions?

Tip: Always double-check the problem's parameters (distances, speeds) and ensure the equation setup aligns with the context.