How much did the Weighted average share price at the grant date change by between 2018 and 2019?
{"Weighted average share price at the grant date": {"2019": 373.33, "2018": 405.0}, "Risk free rate": {"2019": 1.08, "2018": 1.77}, "Dividend yield": {"2019": 0.23, "2018": 0.24}, "Expected volatility (Note)": {"2019": 30.0, "2018": 30.0}}
weighted_avg_2019 = df["Weighted average share price at the grant date"]["2019"]
weighted_avg_2018 = df["Weighted average share price at the grant date"]["2018"]
answer = weighted_avg_2019 - weighted_avg_2018