I think you will find a good explanation of your situation and how to handle it in the link below.
Note: The "basis" for your asset is what you paid for it, plus any significant improvements (those that would be expected to last a long time - like adding an upgraded stereo to it).
The explanation of how to handle this in Turbotax
https://ttlc.intuit.com/community/tax-credits-deductions/discussion/where-do-i-report-income-from-se...
The IRS description of assets and the basis of assets
https://www.irs.gov/taxtopics/tc409
This has a link to Publication 551 Basis of Assets.
