What is a question about this article? If the question is unanswerable, say "unanswerable".

New York City has focused on reducing its environmental impact and carbon footprint. Mass transit use in New York City is the highest in the United States. Also, by 2010, the city had 3,715 hybrid taxis and other clean diesel vehicles, representing around 28% of New York's taxi fleet in service, the most of any city in North America.

How many clean diesel and hybrid taxicabs did New York City have in 2010?
3,715