What was the change in the Additions based on tax positions related to the current year between 2017 and 2018?
{"Beginning balance": {"July 27, 2019": 2000, "July 28, 2018": 1973, "July 29, 2017": 1627}, "Additions based on tax positions related to the current year": {"July 27, 2019": 185, "July 28, 2018": 251, "July 29, 2017": 336}, "Additions for tax positions of prior years": {"July 27, 2019": 84, "July 28, 2018": 84, "July 29, 2017": 180}, "Reductions for tax positions of prior years .": {"July 27, 2019": -283, "July 28, 2018": -129, "July 29, 2017": -78}, "Settlements": {"July 27, 2019": -38, "July 28, 2018": -124, "July 29, 2017": -43}, "Lapse of statute of limitations .": {"July 27, 2019": -23, "July 28, 2018": -55, "July 29, 2017": -49}, "Ending balance .": {"July 27, 2019": 1925, "July 28, 2018": 2000, "July 29, 2017": 1973}}
additions_2018 = df["Additions based on tax positions related to the current year"]["July 28, 2018"]
additions_2017 = df["Additions based on tax positions related to the current year"]["July 29, 2017"]
answer = additions_2018 - additions_2017