What was the change in Fair value of share awards vested in 2019 from 2018?
{"Number of share awards granted": {"2019": 34.0, "2018": 34.0, "2017": 24.0}, "Weighted average grant-date fair value per share award": {"2019": 25.41, "2018": 27.68, "2017": 32.93}, "Fair value of share awards vested": {"2019": 840.0, "2018": 880.0, "2017": 850.0}}
fair_value_of_share_awards_vested_2019 = df["Fair value of share awards vested"]["2019"]
fair_value_of_share_awards_vested_2018 = df["Fair value of share awards vested"]["2018"]
answer = fair_value_of_share_awards_vested_2019 - fair_value_of_share_awards_vested_2018