What is the number of units granted for 2019 expressed as a percentage of all units granted?
{"Number of units granted": {"2019": 70543.0, "2018": 56829.0, "2017": 100958.0}, "Weighted average fair value on grant date(1) (3)": {"2019": 57.53, "2018": 43.4, "2017": 44.24}, "Expected Price volatility(2)": {"2019": 22.86, "2018": 22.0, "2017": 25.31}, "Risk-free interest rate(2)": {"2019": 2.36, "2018": 2.0, "2017": 1.56}}
units_2019 = df["Number of units granted"]["2019"]
units_2018 = df["Number of units granted"]["2018"]
units_2017 = df["Number of units granted"]["2017"]
total_units = units_2019 + units_2018 + units_2017
answer = units_2019 / total_units * 100.0