What was the change in purchased software between 2018 and 2019?
{"Internally developed software": {"2019": 808.2, "2018": 746.0}, "Purchased software": {"2019": 78.9, "2018": 60.7}, "Computer software": {"2019": 887.1, "2018": 806.7}, "Accumulated amortization": {"2019": -481.1, "2018": -401.1}, "Computer software, net": {"2019": 406.0, "2018": 405.6}}
purchased_software_2019 = df["Purchased software"]["2019"]
purchased_software_2018 = df["Purchased software"]["2018"]
answer = purchased_software_2019 - purchased_software_2018