It's usually best to post a new subject, as a new post. More experts will see it.
That said, since you rented it out, you have more issues than just cost basis.
Basically yes, you've done the cost basis correctly. But it has to be entered on the forms in a specific manner. You add the $80,000 to your cost basis. Then enter the depreciation separately for "Depreciation recapture" which is taxed separately (but still subject to offset by capital losses).
When a rental is sold, depreciation "allowed or allowable" must be recaptured. That is, you must recapture the depreciation you didn't claim on the whole house. You may want to amend you 2018 return. You should also include the 2019 depreciation (for the time rented) on your 2019 Schedule E.
