I see it now in the IRA worksheet. It shows a "Basis for 2016 or earlier years" of $6,500." I did have contributions that were not deductible in earlier years. So it appears the difference between the $8,000 2017 distribution and the earlier $6,500 basis is the $1,500 taxable amount. So my line 15b is defendable. Thanks everyone for all your help here.
