What was the percentage change in the Balance at end of fiscal year between 2018 and 2019?
{"Balance at beginning of fiscal year": {"July 27, 2019": 359, "July 28, 2018": 407, "July 29, 2017": 414}, "Provisions for warranties issued": {"July 27, 2019": 600, "July 28, 2018": 582, "July 29, 2017": 691}, "Adjustments for pre-existing warranties": {"July 27, 2019": -12, "July 28, 2018": -38, "July 29, 2017": -21}, "Settlements": {"July 27, 2019": -603, "July 28, 2018": -592, "July 29, 2017": -677}, "Acquisitions and divestitures": {"July 27, 2019": -2, "July 28, 2018": "\u2014", "July 29, 2017": "\u2014"}, "Balance at end of fiscal year": {"July 27, 2019": 342, "July 28, 2018": 359, "July 29, 2017": 407}}
balance_2019 = df["Balance at end of fiscal year"]["July 27, 2019"]
balance_2018 = df["Balance at beginning of fiscal year"]["July 27, 2019"]
answer = (balance_2019 - balance_2018) / balance_2018 * 100.0