What was the change in finished goods between 2018 and 2019?
{"Raw materials": {"2019": 8921, "2018": 6396}, "Finished goods": {"2019": 25247, "2018": 16594}, "Total inventory, net": {"2019": 34168, "2018": 22990}}
finished_goods_2019 = df["Finished goods"]["2019"]
finished_goods_2018 = df["Finished goods"]["2018"]
answer = finished_goods_2019 - finished_goods_2018