What is the percentage change in the average fair value impact of energy commodities from 2018 to 2019?
{"Processing Activities -- Energy commodities": {"Average During the Fiscal Year Ended May 26, 2019": 0.4, "Average During the Fiscal Year Ended May 27, 2018": 0.2}, "Processing Activities -- Agriculture commodities": {"Average During the Fiscal Year Ended May 26, 2019": 0.4, "Average During the Fiscal Year Ended May 27, 2018": 0.4}, "Processing Activities -- Other commodities": {"Average During the Fiscal Year Ended May 26, 2019": 0.1, "Average During the Fiscal Year Ended May 27, 2018": "\u2014"}, "Processing Activities -- Foreign exchange": {"Average During the Fiscal Year Ended May 26, 2019": 0.7, "Average During the Fiscal Year Ended May 27, 2018": 0.7}}
average_fair_value_impact_2019 = df["Processing Activities -- Energy commodities"]["Average During the Fiscal Year Ended May 26, 2019"]
average_fair_value_impact_2018 = df["Processing Activities -- Energy commodities"]["Average During the Fiscal Year Ended May 27, 2018"]
answer = ( average_fair_value_impact_2019 - average_fair_value_impact_2018 ) / average_fair_value_impact_2018 * 100.0