Many major cities have public modes of transportation. London has the Tube, which travels 20.5 miles for every hour. The New York City Subway's speed can be represented by the
equation y 172, where y represents the total distance traveled in miles, and a represents the number of hours the Subway is in transit.
If both the Tube and the Subway travel at constant rates for 3 hours, how much farther has a passenger traveled taking the Tube than the Subway?