What was the change in operating income in 2019 from 2018?
{"Summary of Operations: -- Net sales": {"2019 (a)": 2380.2, "2018(b)": 2157.7, "2017(c)": 1797.6, "2016(d)(f)": 1813.4, "2015 (e)(f)": 2226.7}, "Summary of Operations: -- Operating income": {"2019 (a)": 241.4, "2018(b)": 189.3, "2017(c)": 121.5, "2016(d)(f)": 70.8, "2015 (e)(f)": 119.3}, "Summary of Operations: -- Net income": {"2019 (a)": 167.0, "2018(b)": 188.5, "2017(c)": 47.0, "2016(d)(f)": 11.3, "2015 (e)(f)": 58.7}, "Financial Position at Year-End: -- Cash and cash equivalents": {"2019 (a)": 27.0, "2018(b)": 56.2, "2017(c)": 66.3, "2016(d)(f)": 82.0, "2015 (e)(f)": 70.0}, "Financial Position at Year-End: -- Total assets": {"2019 (a)": 3187.8, "2018(b)": 3007.0, "2017(c)": 2878.1, "2016(d)(f)": 2794.3, "2015 (e)(f)": 2902.6}, "Financial Position at Year-End: -- Long-term debt, net of current portion": {"2019 (a)": 550.6, "2018(b)": 545.7, "2017(c)": 550.0, "2016(d)(f)": 611.3, "2015 (e)(f)": 603.8}, "Net earnings: -- Basic": {"2019 (a)": 3.46, "2018(b)": 3.96, "2017(c)": 0.99, "2016(d)(f)": 0.23, "2015 (e)(f)": 1.11}, "Net earnings: -- Diluted": {"2019 (a)": 3.43, "2018(b)": 3.92, "2017(c)": 0.99, "2016(d)(f)": 0.23, "2015 (e)(f)": 1.11}, "Net earnings: -- Cash dividend-common": {"2019 (a)": 0.8, "2018(b)": 0.72, "2017(c)": 0.72, "2016(d)(f)": 0.72, "2015 (e)(f)": 0.72}, "Weighted Average Common Shares outstanding: -- Basic": {"2019 (a)": 47.7, "2018(b)": 47.2, "2017(c)": 47.0, "2016(d)(f)": 48.1, "2015 (e)(f)": 52.6}, "Weighted Average Common Shares outstanding: -- Diluted": {"2019 (a)": 48.1, "2018(b)": 47.6, "2017(c)": 47.1, "2016(d)(f)": 48.2, "2015 (e)(f)": 52.7}}
summary_of_operations__operating_income_2019_a = df["Summary of Operations: -- Operating income"]["2019 (a)"]
summary_of_operations__operating_income_2018b = df["Summary of Operations: -- Operating income"]["2018(b)"]
answer = summary_of_operations__operating_income_2019_a - summary_of_operations__operating_income_2018b