What was the percentage change in gross goodwill between 2018 and 2019?
{"Adjusted EBITDA": {"2015 2": 3206.0, "2016 3": 3743.0, "2017 4": 4149.0, "2018 4,5": 4725.0, "2019 4": 4917.0}, "Cash Taxes": {"2015 2": -107.0, "2016 3": -98.0, "2017 4": -137.0, "2018 4,5": -172.0, "2019 4": -168.0}, "Maintenance Capex": {"2015 2": -124.0, "2016 3": -159.0, "2017 4": -115.0, "2018 4,5": -150.0, "2019 4": -160.0}, "Corporate Capex": {"2015 2": -26.0, "2016 3": -27.0, "2017 4": -17.0, "2018 4,5": -9.0, "2019 4": -11.0}, "Numerator": {"2015 2": 2948.0, "2016 3": 3459.0, "2017 4": 3880.0, "2018 4,5": 4394.0, "2019 4": 4579.0}, "Gross PPE": {"2015 2": 14397.0, "2016 3": 15652.0, "2017 4": 16950.0, "2018 4,5": 17717.0, "2019 4": 19326.0}, "Gross Intangibles": {"2015 2": 12671.0, "2016 3": 14795.0, "2017 4": 16183.0, "2018 4,5": 16323.0, "2019 4": 18474.0}, "Gross Goodwill6": {"2015 2": 4240.0, "2016 3": 4510.0, "2017 4": 4879.0, "2018 4,5": 4797.0, "2019 4": 5492.0}, "Denominator": {"2015 2": 31308.0, "2016 3": 34957.0, "2017 4": 38012.0, "2018 4,5": 38837.0, "2019 4": 43292.0}, "ROIC": {"2015 2": 9.4, "2016 3": 9.9, "2017 4": 10.2, "2018 4,5": 11.3, "2019 4": 10.6}}
gross_goodwill_2019 = df["Gross Goodwill6"]["2019 4"]
gross_goodwill_2018 = df["Gross Goodwill6"]["2018 4,5"]
answer = (gross_goodwill_2019 - gross_goodwill_2018) / gross_goodwill_2018 * 100.0