What is the percentage change in the weighted-average fair value of options granted in 2019 compared to 2017?
{"Weighted-average fair value ($)": {"2019": 68.05, "2018": 57.75, "2017": 40.87}, "Risk-free interest rate (%)": {"2019": 2.37, "2018": 2.65, "2017": 2.03}, "Average expected option life (years)": {"2019": 5.42, "2018": 5.32, "2017": 5.26}, "Expected volatility (%)": {"2019": 19.22, "2018": 18.05, "2017": 18.74}, "Expected dividend yield (%)": {"2019": 0.58, "2018": 0.59, "2017": 0.67}}
weighted_average_fair_value_2019 = df["Weighted-average fair value ($)"]["2019"]
weighted_average_fair_value_2017 = df["Weighted-average fair value ($)"]["2017"]
answer = (weighted_average_fair_value_2019 - weighted_average_fair_value_2017) / weighted_average_fair_value_2017 * 100.0