What do you call the piece of paper you receive when you buy something

The following information is from the 2019 records of albert book shop: accounts receivable, december 31, 2019 $ 42 comma 000 (debit) allowance for bad debts, december 31, 2019 prior to adjustment 2 comma 000 (debit) net credit sales for 2019 179 comma 000 accounts written off as uncollectible during 2017 15 comma 000 cash sales during 2019 28 comma 500 bad debts expense is estimated by the method. management estimates that $ 5 comma 300 of accounts receivable will be uncollectible. calculate the amount of bad debts expense for 2019.