What was the change in the Average invested capital for the year in 2019 from 2018?
{"Operating profit/(loss) (EBIT)": {"2019": 205.9, "2018": 2.8, "2017": 39.5}, "Tax": {"2019": -0.8, "2018": -1.6, "2017": -0.8}, "EBIT less Tax": {"2019": 205.1, "2018": 1.2, "2017": 38.7}, "Invested capital, opening balance": {"2019": 1469.4, "2018": 1406.0, "2017": 1387.7}, "Invested capital, ending balance": {"2019": 1786.0, "2018": 1469.4, "2017": 1406.0}, "Average invested capital for the year": {"2019": 1627.7, "2018": 1437.7, "2017": 1396.9}, "Return on Invested Capital (RoIC)": {"2019": 12.6, "2018": 0.1, "2017": 2.8}}
average_invested_capital_for_the_year_2019 = df["Average invested capital for the year"]["2019"]
average_invested_capital_for_the_year_2018 = df["Average invested capital for the year"]["2018"]
answer = average_invested_capital_for_the_year_2019 - average_invested_capital_for_the_year_2018