What was the percentage change in Weighted-average price per share between 2019 and 2020?
{"Cash proceeds": {"January 31, 2020": 172.0, "February 1, 2019": 161.0, "February 2, 2018": 65.0}, "Class A common stock purchased": {"January 31, 2020": 1489.0, "February 1, 2019": 1895.0, "February 2, 2018": 903.0}, "Weighted-average price per share": {"January 31, 2020": 115.51, "February 1, 2019": 84.95, "February 2, 2018": 72.4}}
weighted_average_price_per_share_2020 = df["Weighted-average price per share"]["January 31, 2020"]
weighted_average_price_per_share_2019 = df["Weighted-average price per share"]["February 1, 2019"]
answer = (weighted_average_price_per_share_2020 - weighted_average_price_per_share_2019) / weighted_average_price_per_share_2019 * 100.0