What is the change in the adjusted EBITDA margin in 2019?
{"Net earnings": {"2019": 3253.0, "2018": 2973.0}, "Severance, acquisition and other costs": {"2019": 114.0, "2018": 136.0}, "Depreciation": {"2019": 3496.0, "2018": 3145.0}, "Amortization": {"2019": 902.0, "2018": 869.0}, "Finance costs -- Interest expense": {"2019": 1132.0, "2018": 1000.0}, "Finance costs -- Interest on post-employment benefit obligations": {"2019": 63.0, "2018": 69.0}, "Finance costs -- Other expense": {"2019": 13.0, "2018": 348.0}, "Finance costs -- Income taxes": {"2019": 1133.0, "2018": 995.0}, "Finance costs -- Adjusted EBITDA": {"2019": 10106.0, "2018": 9535.0}, "Finance costs -- BCE operating revenues": {"2019": 23964.0, "2018": 23468.0}, "Finance costs -- Adjusted EBITDA margin": {"2019": 42.2, "2018": 40.6}}
adjusted_ebitda_margin_2019 = df["Finance costs -- Adjusted EBITDA margin"]["2019"]
adjusted_ebitda_margin_2018 = df["Finance costs -- Adjusted EBITDA margin"]["2018"]
answer = adjusted_ebitda_margin_2019 - adjusted_ebitda_margin_2018