What was the percentage change in Pre-tax losses on sale of receivables between 2017 and 2018?
{"Trade accounts receivable sold": {"2019(3)": 4057, "2018": 8386, "2017": 8878}, "Cash proceeds received(1)": {"2019(3)": 4031, "2018": 7838, "2017": 8300}, "Pre-tax losses on sale of receivables(2)": {"2019(3)": 26, "2018": 15, "2017": 9}, "Deferred purchase price receivables as of August 31": {"2019(3)": "$\u2014", "2018": 533, "2017": 569}}
pretax_losses_on_sale_of_receivables_2018 = df["Pre-tax losses on sale of receivables(2)"]["2018"]
pretax_losses_on_sale_of_receivables_2017 = df["Pre-tax losses on sale of receivables(2)"]["2017"]
answer = ( pretax_losses_on_sale_of_receivables_2018 - pretax_losses_on_sale_of_receivables_2017 ) / pretax_losses_on_sale_of_receivables_2017 * 100.0