the k-1 comes from you owning some shares in a publicly traded or master limited partnership. so when you sell the reporting gets complicated. you need to enter the k-1 info. the basis/cost that Robinhood shows is most likely incorrect. there should have been a sales schedule along with the k-1 which allows you to compute the correct tax basis and gain. there may be ordinary income to report on the schedule something like form 4797 line 10 in column x. if it was a full disposal you need to check final k-1. you also need to use the k-1 sales section to report the sale so any suspended passive losses are allowed. this is where you report the 4797 income (as sales price) cost = 0 ordinary gain same as on sales schedule. the ordinary gain, if any, adds to your tax basis.
easiest is to reprt the the sale on the 1099-B worksheet but as noted you'll need to adjust cost.
