What is the change in Marketing costs between 2018 and 2019?
{"": {"30 Mar 2019": "\u00a3m", "31 Mar 2018": "\u00a3m", "Change": "%"}, "Store staffing": {"30 Mar 2019": 1044.7, "31 Mar 2018": 1070.6, "Change": -2.4}, "Other store costs": {"30 Mar 2019": 950.4, "31 Mar 2018": 992.1, "Change": -4.2}, "Distribution & warehousing": {"30 Mar 2019": 564.6, "31 Mar 2018": 538.0, "Change": 4.9}, "Marketing": {"30 Mar 2019": 155.1, "31 Mar 2018": 151.6, "Change": 2.3}, "Central costs": {"30 Mar 2019": 694.8, "31 Mar 2018": 698.0, "Change": -0.5}, "Total": {"30 Mar 2019": 3409.6, "31 Mar 2018": 3450.3, "Change": -1.2}}
marketing_2019 = df["Marketing"]["30 Mar 2019"]
marketing_2018 = df["Marketing"]["31 Mar 2018"]
answer = marketing_2019 - marketing_2018