Answer:
Option a: 11.875 miles per hour
Explanation:
We can calculate Colleen's average speed using a rule of three:
She rode a total of 9.5 miles in 0.8 hours, so how much she would rode in 1 hour (this way we can calculate her speed in miles per hour)
9.5 miles -> 0.8 hours
X miles -> 1 hour
9.5/X = 0.8
X = 9.5 / 0.8 = 11.875 miles per hour
The correct option is option "a".