What is the percentage change in the company's gross profit between the fiscal years ended September 2018 and 2019?
{"Sales (including excise taxes of $370.2 million and $368.4 million,": {"2019": 1392388157.0, "2018": 1322306658.0}, "Cost of sales": {"2019": 1308364726.0, "2018": 1245375460.0}, "Gross profit": {"2019": 84023431.0, "2018": 76931198.0}, "Selling, general and administrative expenses": {"2019": 72182883.0, "2018": 66781234.0}, "Depreciation and amortization": {"2019": 2617591.0, "2018": 2318146.0}, "Impairment charges": {"2019": 2873269.0, "2018": 1912877.0}, "": {"2019": 77673743.0, "2018": 71012257.0}, "Operating income": {"2019": 6349688.0, "2018": 5918941.0}, "Other expense (income): -- Interest expense": {"2019": 1598864.0, "2018": 1194373.0}, "Other expense (income): -- Other (income), net": {"2019": -61119.0, "2018": -54042.0}, "Other expense (income): -- ": {"2019": 1537745.0, "2018": 1140331.0}, "Other expense (income): -- Income from operations before income taxes": {"2019": 4811943.0, "2018": 4778610.0}, "Other expense (income): -- Income tax expense": {"2019": 1609000.0, "2018": 1164000.0}, "Other expense (income): -- Net income available to common shareholders": {"2019": 3202943.0, "2018": 3614610.0}, "Other expense (income): -- Basic earnings per share available to common shareholders": {"2019": 5.36, "2018": 5.47}, "Other expense (income): -- Diluted earnings per share available to common shareholders": {"2019": 5.25, "2018": 5.38}, "Other expense (income): -- Basic weighted average shares outstanding": {"2019": 597961.0, "2018": 660925.0}, "Other expense (income): -- Diluted weighted average shares outstanding": {"2019": 609836.0, "2018": 672449.0}, "Other expense (income): -- Dividends declared and paid per common share": {"2019": 1.0, "2018": 1.0}}
gross_profit_2019 = df["Gross profit"]["2019"]
gross_profit_2018 = df["Gross profit"]["2018"]
answer = ( gross_profit_2019 - gross_profit_2018 ) / gross_profit_2018 * 100.0