What was the change in the U.S. state taxes, net of federal from 2018 to 2019?
{"Tax at statutory rate": {"2019": 19.0, "2018": 19.0, "2017": 20.0}, "U.S. state taxes, net of federal": {"2019": 31.1, "2018": 14.1, "2017": -1.0}, "Foreign rate differential  ": {"2019": 26.3, "2018": 36.8, "2017": -39.3}, "Meals and entertainment  ": {"2019": -11.4, "2018": -3.1, "2017": -7.4}, "Branch income / loss  ": {"2019": -0.6, "2018": 0.4, "2017": 0.9}, "Share-based compensation": {"2019": 172.3, "2018": 105.3, "2017": -4.0}, "Foreign exchange  ": {"2019": "\u2014", "2018": "\u2014", "2017": -24.8}, "Non-deductible interest expense  ": {"2019": "\u2014", "2018": "\u2014", "2017": -3.3}, "Tax credits": {"2019": 7.7, "2018": 8.1, "2017": 15.6}, "Unremitted earnings  ": {"2019": -3.8, "2018": -1.2, "2017": "\u2014"}, "Change in valuation allowance  ": {"2019": -249.9, "2018": -110.7, "2017": 124.7}, "Deferred tax true-ups  ": {"2019": -3.5, "2018": 8.4, "2017": -12.4}, "Tax reserves  ": {"2019": -4.9, "2018": -21.5, "2017": -117.7}, "Provision to return  ": {"2019": -0.1, "2018": 0.4, "2017": -0.7}, "Withholding taxes  ": {"2019": -2.6, "2018": -3.5, "2017": "\u2014"}, "Other foreign taxes  ": {"2019": "\u2014", "2018": "\u2014", "2017": -6.7}, "Non-deductible expenses  ": {"2019": -5.2, "2018": -2.4, "2017": -10.6}, "Deferred tax rate change  ": {"2019": -6.3, "2018": -77.8, "2017": -1.3}, "Acquisition related costs  ": {"2019": -7.6, "2018": "\u2014", "2017": "\u2014"}, "Other  ": {"2019": -0.5, "2018": -0.2, "2017": "\u2014"}, "Effective Tax Rate  ": {"2019": -40.0, "2018": -27.9, "2017": -68.0}}
us_state_taxes_net_of_federal_2019 = df["U.S. state taxes, net of federal"]["2019"]
us_state_taxes_net_of_federal_2018 = df["U.S. state taxes, net of federal"]["2018"]
answer = us_state_taxes_net_of_federal_2019 - us_state_taxes_net_of_federal_2018