What is the value of R&D expenses as a percentage of the cost of revenues in 2018?
{"Revenues": {"2018": 82.3, "2017": 50.5, "Change": 31.8, "% Change": 63.0}, "Cost of revenues": {"2018": 15.3, "2017": 6.0, "Change": 9.3, "% Change": 155.0}, "Gross profit": {"2018": 67.0, "2017": 44.5, "Change": 22.5, "% Change": 51.0}, "Operating expenses: -- Selling, general and administrative": {"2018": 32.2, "2017": 28.6, "Change": 3.6, "% Change": 13.0}, "Operating expenses: -- Research and development": {"2018": 2.1, "2017": 1.5, "Change": 0.6, "% Change": 40.0}, "Operating expenses: -- Total operating expenses": {"2018": 34.3, "2017": 30.1, "Change": 4.2, "% Change": 14.0}, "Operating expenses: -- Other income (expense)": {"2018": -4.0, "2017": 2.2, "Change": -6.2, "% Change": -282.0}, "Operating expenses: -- Income before income taxes": {"2018": 28.7, "2017": 16.6, "Change": 12.1, "% Change": 73.0}, "Operating expenses: -- Income tax provision (benefit)": {"2018": 8.0, "2017": -6.2, "Change": 14.2, "% Change": -229.0}, "Operating expenses: -- Net income": {"2018": 20.7, "2017": 22.8, "Change": -2.1, "% Change": -9.0}}
rd_expenses_2018 = df["Operating expenses: -- Research and development"]["2018"]
revenue_cost_2018 = df["Cost of revenues"]["2018"]
answer = rd_expenses_2018 / revenue_cost_2018 * 100.0