Final answer:
Shelby and her father's approximate average speed for their trip from St. Louis to Chicago is 60.7 miles per hour (mph), based on the formula for average speed which is distance divided by time. This corresponds to option (a).
Step-by-step explanation:
To find Shelby and her father's approximate average speed for their trip from St. Louis to Chicago, we need to use the formula for average speed, which is the total distance traveled divided by the total time of travel. In this case, the distance is 728 miles and the time is approximately 12 hours.
The formula for calculating average speed (Vavg) is:
Vavg = distance ÷ time
Inserting the given values:
Vavg = 728 miles ÷ 12 hours
Vavg = 60.7 mph
Therefore, the approximate average speed for their trip is 60.7 miles per hour (mph), which corresponds to option (a).