What is the percentage change of amount of inventory from 2018 and 2019 ?
{"Raw Materials and Component Parts": {"2019": 11600, "2018": 16206}, "Work in Progress": {"2019": 8896, "2018": 8216}, "Finished Goods": {"2019": 2860, "2018": 1764}, "": {"2019": 23356, "2018": 26186}}
inventory_2019 = df[""]["2019"]
inventory_2018 = df[""]["2018"]
answer = ( inventory_2019 - inventory_2018 ) / inventory_2018 * 100.0