To solve this problem, we need to calculate how many miles Louise has walked, given that she has completed 3/4 of a 12-mile walk.

We can use the formula:

$\text{Miles walked} = \text{Total miles} \times \frac{3}{4}$

Substitute the values:

$\text{Miles walked} = 12 \times \frac{3}{4} = \frac{36}{4} = 9 \, \text{miles}$

Therefore, Louise has walked 9 miles.

The correct answer is 9 miles.

Do you need further clarification on this solution, or is there something else you'd like to explore? Here are a few related questions:

1. How would you calculate the remaining distance if she has already walked 9 miles?
2. If she were to walk 5/6 of the total distance, how many miles would that be?
3. What if the total distance was 15 miles instead of 12 miles, how would that change the result?
4. How do you convert fractions like 3/4 to decimals for easier calculation?
5. How can you set up a proportion to solve similar walking or distance problems?

Tip: Fractions can be easily multiplied with whole numbers by first multiplying the numerator (top number) by the whole number, then dividing by the denominator (bottom number).