A hiker is exploring a trail. The trail has three sections: the first 25 \% of the trail is along a river, the next \frac{5}{8} of the trail is through a forest, and the remaining 3 \mathrm{~km} of the trail is up a hill. How long is the trail?
Answer Choices
A. 24 \mathrm{~km}
B. 3 \frac{3}{7} \mathrm{~km}
C. 12 \mathrm{~km}
D. 15 \mathrm{~km}
E. 10 \frac{3}{8} \mathrm{~km}