What was the change in Provisions for warranties issued between 2017 and 2018?
{"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}}
provision_2018 = df["Provisions for warranties issued"]["July 28, 2018"]
provision_2017 = df["Provisions for warranties issued"]["July 29, 2017"]
answer = provision_2018 - provision_2017