Hi there! So 8:18 and 8:48 is 30 minutes apart, and in that time period, the bicyclist went 7.5 miles. 30 minutes is 1/2 an hour, so we can multiply the amount of miles traveled by 2 to get the speed per hour. 7.5 * 2 is 15. The bicyclist’s average speed is 15 miles per hour.