What was the change in raw materials between 2018 and 2019?
{"Raw materials": {"2019": 36987, "2018": 45333}, "Work in process": {"2019": 1085, "2018": 1638}, "Finished goods": {"2019": 60233, "2018": 52877}, "Total Inventory, net": {"2019": 98305, "2018": 99848}}
raw_material_2019 = df["Raw materials"]["2019"]
raw_material_2018 = df["Raw materials"]["2018"]
answer = raw_material_2019 - raw_material_2018