pre_text: Stock Options—Stock options are typically granted at prices not less than 100% of market value of the underlying stock at the date of grant. Stock options typically vest over a period of 3 to 5 years from the grant date and expire 10 years after the grant date. The Company recorded $32.0, $23.2, and $18.3 of compensation expense relating to outstanding options during 2019, 2018 and 2017, respectively, as a component of general and administrative expenses at Corporate. The Company estimates the fair value of its option awards using the Black-Scholes option valuation model. The stock volatility for each grant is measured using the weighted-average of historical daily price changes of the Company’s common stock over the most recent period equal to the expected life of the grant. The expected term of options granted is derived from historical data to estimate option exercises and employee forfeitures, and represents the period of time that options granted are expected to be outstanding. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. The weighted-average fair value of options granted in 2019, 2018 and 2017 were calculated using the following weighted-average assumptions:
table: 2019 2018 2017
table: Weighted-average fair value ($) 68.05 57.75 40.87
table: Risk-free interest rate (%) 2.37 2.65 2.03
table: Average expected option life (years) 5.42 5.32 5.26
table: Expected volatility (%) 19.22 18.05 18.74
table: Expected dividend yield (%) 0.58 0.59 0.67
question: Analyse this data from a financial earnings document. What is the average weighted-average fair value of options granted from 2017 to 2019?