Investors & landlords

Line 20 of FORM 4797 shows $100 for SALES PRICE (see image I uploaded). Line 21 somehow has $10 for COST  OR OTHER BASIS, and Line 22 has $10 for DEPRECIATION ALLOWED. (So I did enter $100, not $10. TT somehow calculated that $10, but I can;t see where, or how? I was hoping you knew).