What is the percentage change in the offering grant date fair value of ESPP rights between 2018 and 2019?
{"Expected term (in years)": {"2019": 0.5, "2018": 0.5, "2017": 0.5}, "Expected volatility": {"2019": 47.0, "2018": 42.0, "2017": 34.0}, "Risk-free interest rate": {"2019": 2.01, "2018": 2.31, "2017": 1.2}, "Expected dividend yield": {"2019": 0.0, "2018": 0.0, "2017": 0.0}, "Offering grant date fair value of ESPP rights": {"2019": 33.66, "2018": 18.07, "2017": 9.52}}
offering_grant_date_fair_value_of_ESPP_rights_2019 = df["Offering grant date fair value of ESPP rights"]["2019"]
offering_grant_date_fair_value_of_ESPP_rights_2018 = df["Offering grant date fair value of ESPP rights"]["2018"]
answer = ( offering_grant_date_fair_value_of_ESPP_rights_2019 - offering_grant_date_fair_value_of_ESPP_rights_2018 ) / offering_grant_date_fair_value_of_ESPP_rights_2018 * 100.0