What was the percentage change in the value at 31 March in 2019 from 2018?
{"": {"31 March 2019": "$M", "31 March 2018": "$M"}, "At 1 April": {"31 March 2019": 0.9, "31 March 2018": 0.4}, "Charge for the year": {"31 March 2019": 0.6, "31 March 2018": 0.6}, "Amounts written off": {"31 March 2019": -0.2, "31 March 2018": -0.1}, "Effects of movements in exchange rates": {"31 March 2019": -0.1, "31 March 2018": "\u2013"}, "At 31 March": {"31 March 2019": 1.2, "31 March 2018": 0.9}}
value_2019 = df["At 31 March"]["31 March 2019"]
value_2018 = df["At 1 April"]["31 March 2019"]
answer = (value_2019 - value_2018) / value_2018 * 100.0