Answer : The bicyclist's average rate of speed in miles per hour is 15 mile/hr.
Explanation:
Average rate if speed : It is defined as the ratio total distance to total time.
Formula used :

As per question,
Total distance traveled by bicyclist = 4.5 mile + 7.5 mile = 12 mile
Total time taken by bicyclist = (8:48 A.M - 8:00 A.M) = 48 min = 0.8 hr
conversion used : ( 1 hour = 60 minute)
Now put all the given values in the above formula, we get the bicyclist's average rate of speed in miles per hour.


Therefore, the bicyclist's average rate of speed in miles per hour is 15 mile/hr.