If you rented out the property in 2016, in order to correctly report that rental property income/expenses on your 2016 tax return, you had to have the cost basis of the property. So dig out your copy of your 2016 tax return and look for the IRS Form 4562 for that property. There are three of them for that property, and you want the one specifically titled "Amortization and Depreciation Report". Add together the amounts in the Cost (Net of Land) column and the Land column, and that's your cost basis of the property.
