What is the percentage change in the weighted average grant date fair value per share between 2018 and 2019?
{"Non-vested at March 31, 2018": {"Number of shares": 358.0, "Weighted-Average Grant Date Fair Value per Share": 16.27}, "Granted": {"Number of shares": 315.0, "Weighted-Average Grant Date Fair Value per Share": 15.28}, "Vested": {"Number of shares": -172.0, "Weighted-Average Grant Date Fair Value per Share": 16.27}, "Cancelled and forfeited": {"Number of shares": -68.0, "Weighted-Average Grant Date Fair Value per Share": 16.27}, "Non-vested at March 31, 2019": {"Number of shares": 433.0, "Weighted-Average Grant Date Fair Value per Share": 15.55}}
weighted_avg_2019 = df["Non-vested at March 31, 2019"]["Weighted-Average Grant Date Fair Value per Share"]
weighted_avg_2018 = df["Non-vested at March 31, 2018"]["Weighted-Average Grant Date Fair Value per Share"]
answer = (weighted_avg_2019 - weighted_avg_2018) / weighted_avg_2018 * 100.0