What was the change in the value of finished products from 2018 to 2019?
{"Finished Products": {"April 27, 2019": 40.2, "April 28, 2018": 15.4}, "Work in Process": {"April 27, 2019": 9.4, "April 28, 2018": 14.6}, "Materials": {"April 27, 2019": 67.1, "April 28, 2018": 54.1}, "Total Inventories": {"April 27, 2019": 116.7, "April 28, 2018": 84.1}}
finished_products_april_27_2019 = df["Finished Products"]["April 27, 2019"]
finished_products_april_28_2018 = df["Finished Products"]["April 28, 2018"]
answer = finished_products_april_27_2019 - finished_products_april_28_2018