What was the percentage change of the balance at the end between 2018 and 2019?
{"Gross amount at beginning": {"2019": 15960.1, "2018": 15349.0, "2017": 14277.0}, "Additions during period: -- Acquisitions": {"2019": 887.0, "2018": 721.4, "2017": 499.7}, "Additions during period: -- Discretionary capital projects (1)": {"2019": 258.1, "2018": 173.5, "2017": 120.7}, "Additions during period: -- Discretionary ground lease purchases (2)": {"2019": 189.8, "2018": 180.4, "2017": 150.4}, "Additions during period: -- Redevelopment capital expenditures (3)": {"2019": 213.6, "2018": 177.3, "2017": 138.8}, "Additions during period: -- Capital improvements (4)": {"2019": 161.2, "2018": 94.0, "2017": 65.6}, "Additions during period: -- Start-up capital expenditures (5)": {"2019": 71.3, "2018": 113.1, "2017": 158.1}, "Additions during period: -- Other (6)": {"2019": 45.2, "2018": -3.0, "2017": 106.4}, "Additions during period: -- Total additions": {"2019": 1826.2, "2018": 1456.7, "2017": 1239.7}, "Deductions during period: -- Cost of real estate sold or disposed": {"2019": -304.6, "2018": -395.7, "2017": -246.5}, "Deductions during period: -- Other (7)": {"2019": -52.4, "2018": -449.9, "2017": 78.8}, "Deductions during period: -- Total deductions:": {"2019": -357.0, "2018": -845.6, "2017": -167.7}, "Deductions during period: -- Balance at end": {"2019": 17429.3, "2018": 15960.1, "2017": 15349.0}}
balance_2019 = df["Deductions during period: -- Balance at end"]["2019"]
balance_2018 = df["Gross amount at beginning"]["2019"]
answer = (balance_2019 - balance_2018) / balance_2018 * 100.0