13. For more than 35 years, Thelma owned a building that contains a large retail store. She sold the building in 2020 to Louise for $16 million. The building has both a 20-year lease (the owner of the store is the tenant) and a mortgage with a balance of $6 million. The terms are as follows: Louise purchased the building subject to the lease and also assumed Thelmas mortgage on the building and will pay Thelma $1 million per year, starting in 2021, for ten years, together with adequate stated interest. Thelmas adjusted basis in the building is $9 million, but she has claimed depreciation over the years totaling $3 million, of which $1 million is accelerated depreciation. Assuming Thelma decides not to elect out of the installment method, how much gain must she report, if any, in 2020, and what is the nature of any such gain?