The total amount of this RMD seems to be  added to the result from line 18 , to be included on line 15b of my 1040.  Why wouldn't it be included on form 8606?  and if not, should I subtract the yearend value it from line 6 on the 8606 form?

I really don't know if the inherited IRA was non-taxed, but I don't have any way of finding out for sure.   thanks for your reply.

fanfare is correct - You cannot, by law, combine your personal IRA 8606 basis with the basis (if any) in a non-spouse inherited IRA.  They must be kept separate on a stand-alone 8606 that cannot be e-filed with TurboTax.  The inherited IRA 8606 must be completed manually and attached to a mailed tax return.