Tina is training for a biathlon. To train for the running portion of the race, she runs 7 miles each day over the same course. The first 3 miles of the course is on level ground, while the last 4 miles is downhill. She runs 5 miles per hour slower on level ground than she runs downhill. If the complete course takes 1 hour, how fast does she run on the downhill part of the course?

She runs the downhill portion of the course at _____ miles per hour.

This is a proportions math problem.