What was the change in the impact on Equity from a 10% movement in sterling to US dollar value in 2019 from 2018?
{"": {"Year-ended 31 March 2019": "$M", "Year-ended 31 March 2018": "$M"}, "10% movement in sterling to US dollar value -- Profit or loss": {"Year-ended 31 March 2019": 1.7, "Year-ended 31 March 2018": 5.1}, "10% movement in sterling to US dollar value -- Equity": {"Year-ended 31 March 2019": 33.8, "Year-ended 31 March 2018": 37.4}, "10% movement in euro to US dollar value -- Profit or loss": {"Year-ended 31 March 2019": 1.5, "Year-ended 31 March 2018": 7.5}, "10% movement in euro to US dollar value -- Equity": {"Year-ended 31 March 2019": -9.8, "Year-ended 31 March 2018": -10.8}}
ten_percent_movement_in_sterling_to_us_dollar_value_equity_yearended_31_march_2019 = df["10% movement in sterling to US dollar value -- Equity"]["Year-ended 31 March 2019"]
ten_percent_movement_in_sterling_to_us_dollar_value_equity_yearended_31_march_2018 = df["10% movement in sterling to US dollar value -- Equity"]["Year-ended 31 March 2018"]
answer = ten_percent_movement_in_sterling_to_us_dollar_value_equity_yearended_31_march_2019 - ten_percent_movement_in_sterling_to_us_dollar_value_equity_yearended_31_march_2018