Answer:
Sarah must has to ride with average speed 10 miles per hour.
Step-by-step explanation:
Average Speed tells the rate at which object is travelling his whole journey.
[tex]Average\ Speed\=\ \frac{Total\ distance\ traveled}{Total\ time\ taken}[/tex]
∴ [tex]Average\ Speed=\dfrac{2.5}{\frac{15}{60}}[/tex]
⇒ [tex]Average\ Speed=\dfrac{2.5}{15}\times 60[/tex]
⇒ Average Speed = 10 miles per hour
Hence, Sarah has to travel with average speed more than 10 miles per hour.