What is the sum of additions and accretion expense in 2018?
{"Beginning balance as of January 1,": {"2019": 1210.0, "2018": 1175.3}, "Additions": {"2019": 61.8, "2018": 39.6}, "Accretion expense": {"2019": 81.6, "2018": 83.6}, "Revisions in estimates (1)": {"2019": 56.8, "2018": -81.5}, "Settlements": {"2019": -26.1, "2018": -7.0}, "Balance as of December 31,": {"2019": 1384.1, "2018": 1210.0}}
additions_2018 = df["Additions"]["2018"]
accretion_expense_2018 = df["Accretion expense"]["2018"]
answer = additions_2018 + accretion_expense_2018