Yes. However, "estimated" applies to the number (in this case 3 million); you can't just say "an estimated people" or "an estimated houses" or whatever.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
moon7296The article "an" is not optional but mandatory?An article or other determiner is necessary. It does not always have to be "an" -- although "an" is probably most usual.