Trains are up to sixteen cars long. With each car measuring 25 m (82 ft) in length, the longest trains are 400 m (1⁄4 mile) end to end. Stations are similarly long to accommodate these trains. Some of Japan's high-speed maglev trains are considered Shinkansen, while other slower maglev trains (such as the Linimo maglev train line serving local community near the city of Nagoya in Aichi, Japan) are intended as alternatives to conventional urban rapid transit systems.
https://en.wikipedia.org/wiki/Shinkansen
Based on this paragraph on Japanese bullet trains, how many cars do the longest trains have?
Based on this paragraph, the longest Japanese bullets trains have 16 cars, which is determined by dividing the length of the longes trains (400m) by the length of each car (25m).