Work through the sale again. There's a "learn more" link next to "Fair Market Value on Date of Gift". Click it. It reads:
The cost or basis of property is usually the original cost of the property, adjusted for various items after you acquired it. Additions to basis include improvements you made to the property and nondeductible assessments for improvement.
Therefore you will add the cost of the property improvements you did, to the amount in this box.
If you click the "learn more" link next to Donor's cost basis, you'll see the same applies to this box also.
