What was the percentage change in Income tax expense between 2018 and 2019?
{"Net sales ": {"2019": 3164.4, "2018": 2873.5}, "Cost of sales ": {"2019": 2872.6, "2018": 2615.9}, "Gross profit ": {"2019": 291.8, "2018": 257.6}, "Gross margin ": {"2019": 9.2, "2018": 9.0}, "Operating income ": {"2019": 142.1, "2018": 118.3}, "Operating margin ": {"2019": 4.5, "2018": 4.1}, "Other expense ": {"2019": 16.1, "2018": 10.7}, "Income tax expense": {"2019": 17.3, "2018": 94.6}, "Net income ": {"2019": 108.6, "2018": 13.0}, "Diluted earnings per share ": {"2019": 3.5, "2018": 0.38}, "Return on invested capital* ": {"2019": 13.1, "2018": 16.1}, "Economic return*": {"2019": 4.1, "2018": 6.6}}
income_tax_expense_2019 = df["Income tax expense"]["2019"]
income_tax_expense_2018 = df["Income tax expense"]["2018"]
answer = (income_tax_expense_2019 - income_tax_expense_2018) / income_tax_expense_2018 * 100.0