how do I tell which 3.5 engine is in my 2007 impala LT on 2007 Chevrolet Impala

need to know the difference between the flex fuel and regular engine

2 answers
Owners manual, information and emissions labels under hood, badges on car body or call dealer with/google vin #, yellow gas cap, sticker inside the fuel door for a couple more ways to tell. Look around you will find it! If you do not find any of these giveaway's, it aint FF!!
Contact me with the VIN and I will be able to tell you. autoknowhow@gmail.com