What is the change in Net accounts receivable from December 31, 2019 to December 31, 2018?
{"Accounts receivable": {"2019": 69767, "2018": 41818}, "Allowance for doubtful accounts": {"2019": -1125, "2018": -711}, "Net accounts receivable": {"2019": 68642, "2018": 41107}}
net_accounts_receivable_2019 = df["Net accounts receivable"]["2019"]
net_accounts_receivable_2018 = df["Net accounts receivable"]["2018"]
answer = net_accounts_receivable_2019 - net_accounts_receivable_2018