Final answer:
The maximum speed limit for a train traveling through an under river tunnel is 80 MPH.
Step-by-step explanation:
The rules state that a train operator traveling through an under river tunnel is limited to a maximum speed of 80 MPH.
The given information mentions that the train travels 40 miles one way and 40 miles back, for a total distance of 80 miles. To calculate the average speed, we divide the total distance by the total time taken.
Let's assume that the total time taken to travel 80 miles is T. Using the formula Average Speed = Total Distance / Total Time, we can calculate the average speed as 80 / T miles per hour.