Visit www.sec.gov/edgar and search for the Delta Air Lines annual report (10-K) for the year ended December 31, 2018, using EDGAR (Electronic Data Gathering, Analysis, and Retrieval system). Locate the note titled "Revenue Recognition."\\n\\nRequired:\\nWhat percent of total passenger revenue in 2018 came from ticket sales?\\nNote: Round your answer to the nearest whole percentage.\\nIn which liability account does Delta record the sales of passenger tickets for flights that have not yet flown?\\nWhen does Delta recognize revenue of tickets that were purchased, but never used?