What is the percentage of expenses that went towards stock-based compensation in 2019?
{"Year Ended May 31, -- ": {"2019": "", "Actual": "", "Constant": "Percent Change", "2018": ""}, "Year Ended May 31, -- (Dollars in millions)": {"2019": 2019, "Actual": "Actual", "Constant": "Constant", "2018": 2018}, "Year Ended May 31, -- Research and development (1)": {"2019": 5063, "Actual": -2, "Constant": 0, "2018": 5163}, "Year Ended May 31, -- Stock-based compensation": {"2019": 963, "Actual": 5, "Constant": 5, "2018": 921}, "Year Ended May 31, -- Total expenses": {"2019": 6026, "Actual": -1, "Constant": 0, "2018": 6084}, "Year Ended May 31, -- % of Total Revenues": {"2019": 15, "Actual": "", "Constant": "", "2018": 15}}
stockbased_compensation_2019 = df["Year Ended May 31, -- Stock-based compensation"]["2019"]
total_expenses_2019 = df["Year Ended May 31, -- Total expenses"]["2019"]
answer = stockbased_compensation_2019 / total_expenses_2019 * 100.0