1. **State the problem:** We have two similar triangles. The smaller triangle has sides 1 mile and 2 miles, and the larger triangle has a side of 12 miles and a missing side length $s$. We need to find $s$. 2. **Recall the property of similar triangles:** Corresponding sides of similar triangles are proportional. This means the ratio of one side in the smaller triangle to its corresponding side in the larger triangle is equal to the ratio of the other corresponding sides. 3. **Set up the proportion:** Let the side of length 1 mile in the smaller triangle correspond to the side of length 12 miles in the larger triangle. Then the side of length 2 miles in the smaller triangle corresponds to the side $s$ in the larger triangle. So, $$\frac{1}{12} = \frac{2}{s}$$ 4. **Solve for $s$:** Cross-multiply: $$1 \times s = 12 \times 2$$ $$s = 24$$ 5. **Answer:** The missing length $s$ is 24 miles.