Answer: 54.4 mph
Explanation:
First find the distance to the train station. If it took Carlos 4 hours to come back driving at 68 mph, the distance is:
= Speed * time
= 68 * 4
= 272 miles
This means that Carlos drove for 5 hours to cover 272 miles the first time. His average speed was therefore:
= Distance / time
= 272/5
= 54.4 mph