What is the value of the 2018 stock-based compensation for selling, general and administrative as a percentage of the 2019 stock-based compensation for selling, general and administrative?
{"Cost of revenue": {"2019": 78, "2018": 129, "2017": 121}, "Research and development": {"2019": 2242, "2018": 760, "2017": 614}, "Selling, general and administrative": {"2019": 824, "2018": 1012, "2017": 706}, "Total costs and expenses": {"2019": 3144, "2018": 1901, "2017": 1441}}
selling_general_and_administrative_2018 = df["Selling, general and administrative"]["2018"]
selling_general_and_administrative_2019 = df["Selling, general and administrative"]["2019"]
answer = selling_general_and_administrative_2018 / selling_general_and_administrative_2019 * 100.0