What is the change in the amount of total restructuring costs in 2019 from 2018?
{"Restructuring costs: -- Cubic Transportation Systems": {"2019": 3.2, "2018": 0.4, "2017": 0.4}, "Restructuring costs: -- Cubic Mission Solutions": {"2019": "\u2014", "2018": 0.2, "2017": "\u2014"}, "Restructuring costs: -- Cubic Global Defense": {"2019": 3.3, "2018": 1.3, "2017": 0.9}, "Restructuring costs: -- Unallocated corporate expenses": {"2019": 8.9, "2018": 3.1, "2017": 1.0}, "Restructuring costs: -- Total restructuring costs": {"2019": 15.4, "2018": 5.0, "2017": 2.3}}
total_restructuring_costs_2019 = df["Restructuring costs: -- Total restructuring costs"]["2019"]
total_restructuring_costs_2018 = df["Restructuring costs: -- Total restructuring costs"]["2018"]
answer = total_restructuring_costs_2019 - total_restructuring_costs_2018