Answer:
2.5 hours (2 and 1/2)
Explanation:
Every 1 hour, Erin runs 10 miles and so on. The ratio is 1:10 (2:20, 3:30, etc.) 25 is 20+5, and 5 is considered 1/2 of 10, so it would count as 0.5 (or 1/2). So in 2.5 hours Erin will run 25 miles. Hope it helped :>