What was risk-free interest rate in 2017 as a percentage of risk-free interest rate in 2018?
{"Expected life (years)": {"2018": 5.6, "2017": 5.6}, "Risk-free interest rate": {"2018": 2.7, "2017": 1.9}, "Expected volatility": {"2018": 26.4, "2017": 29.4}, "Expected dividend yield": {"2018": "\u2014", "2017": "\u2014"}}
riskfree_interest_rate_2017 = df["Risk-free interest rate"]["2017"]
riskfree_interest_rate_2018 = df["Risk-free interest rate"]["2018"]
answer = riskfree_interest_rate_2017 / riskfree_interest_rate_2018 * 100.0