What is the change in the gross margin % from 2018 to 2019?
{"Total cost of revenue": {"2019": 1058097.0, "2018": 1025419.0, "2017": 864909.0, "2019 % Change from 2018": 3.2, "2018 % Change from 2017": 18.6}, "Gross profit": {"2019": 713580.0, "2018": 724543.0, "2017": 632799.0, "2019 % Change from 2018": -1.5, "2018 % Change from 2017": 14.5}, "Gross margin %": {"2019": 40.3, "2018": 41.4, "2017": 42.3, "2019 % Change from 2018": "", "2018 % Change from 2017": ""}}
gross_margin_percent_2019 = df["Gross margin %"]["2019"]
gross_margin_percent_2018 = df["Gross margin %"]["2018"]
answer = gross_margin_percent_2019 - gross_margin_percent_2018