Where to submit a RFE response

I am going to submit my response to a RFE. At the end of my RFE, it says "please use the enclosed envelope for mailing this evidence back to this office". But I didn't get any enclosed envelope at all. I checked www.cis.gov but I didn't see the mailing address for response to RFE. My center is NSC. Anyone knows it? Please help me! Thanks.