What was the percentage change in the Purchases of property, equipment and software between 2018 and 2019?
{"Software": {"2019": 12.7, "2018": 5.4, "2017": 2.3}, "Computer hardware": {"2019": 1.2, "2018": 0.8, "2017": 0.8}, "Leasehold improvements": {"2019": 0.9, "2018": 0.2, "2017": 0.5}, "Furniture": {"2019": 0.6, "2018": 0.2, "2017": 0.5}, "Purchases of property, equipment and software": {"2019": 15.4, "2018": 6.6, "2017": 4.1}}
purchases_2019 = df["Purchases of property, equipment and software"]["2019"]
purchases_2018 = df["Purchases of property, equipment and software"]["2018"]
answer = ( purchases_2019 - purchases_2018 ) / purchases_2018 * 100.0