Taxpayer A, participated in day-trading throughout the 2021 tax year, including many short sales. A relies on his on-line trading platform to keep track of As stock, sales, dividends and interest received. Unfortunately, the trading platform used by A, called Cinderella, went bankrupt towards the end of the year and did not provide A with a form 1099-B for 2021. A has kept only scant records of his on-line transactions. What should A do?