What was the change in the basic net earnings attributable to Black Knight between 2017 and 2018?
{"Basic: -- Net earnings attributable to Black Knight": {"2019": 108.8, "2018": 168.5, "2017": 182.3}, "Shares used for basic net earnings per share: -- Weighted average shares of common stock outstanding": {"2019": 147.7, "2018": 147.6, "2017": 88.7}, "Shares used for basic net earnings per share: -- Basic net earnings per share": {"2019": 0.74, "2018": 1.14, "2017": 2.06}, "Diluted: -- Earnings before income taxes and equity in losses of unconsolidated affiliates": {"2019": "", "2018": "", "2017": 192.4}, "Diluted: -- Income tax benefit excluding the effect of noncontrolling interests": {"2019": "", "2018": "", "2017": -32.2}, "Diluted: -- Net earnings": {"2019": "", "2018": "", "2017": 224.6}, "Diluted: -- Net earnings attributable to Black Knight": {"2019": 108.8, "2018": 168.5, "2017": ""}, "Shares used for diluted net earnings per share: -- Weighted average shares of common stock outstanding": {"2019": 147.7, "2018": 147.6, "2017": 88.7}, "Dilutive effect of unvested restricted shares of common -- stock": {"2019": 0.9, "2018": 0.6, "2017": 0.6}, "Dilutive effect of unvested restricted shares of common -- Weighted average shares of BKFS Class B common stock outstanding": {"2019": "\u2014", "2018": "\u2014", "2017": 63.1}, "Dilutive effect of unvested restricted shares of common -- Weighted average shares of common stock, diluted": {"2019": 148.6, "2018": 148.2, "2017": 152.4}, "Dilutive effect of unvested restricted shares of common -- Diluted net earnings per share": {"2019": 0.73, "2018": 1.14, "2017": 1.47}}
net_earnings_2018 = df["Basic: -- Net earnings attributable to Black Knight"]["2018"]
net_earnings_2017 = df["Basic: -- Net earnings attributable to Black Knight"]["2017"]
answer = net_earnings_2018 - net_earnings_2017