What was the change in raw materials between 2018 and 2019?
{"Raw materials": {"2019": 74.5, "2018": 26.0}, "Work in process": {"2019": 413.0, "2018": 311.8}, "Finished goods": {"2019": 224.2, "2018": 138.4}, "Total inventories": {"2019": 711.7, "2018": 476.2}}
raw_material_2019 = df["Raw materials"]["2019"]
raw_material_2018 = df["Raw materials"]["2018"]
answer = raw_material_2019 - raw_material_2018