With 2004 revenues of $3.6 billion, there is a lot of business behind the frosted doughnuts and hot coffee. Dunkin' Donuts, in more than 50 years, has grown from a single location in Quincy to roughly 6,200 stores in more than 40 countries. That expansion hasn't slowed. The chain, which opens an average of 600 locations each year, plans to triple its stores nationwide by 2025.