What is the change in the amount for Usage in 2019?
{"Balance, January 1": {"NOTE": "", "2019": -51, "2018": -54}, "Adoption of IFRS 9": {"NOTE": "", "2019": "\u2013", "2018": -4}, "Additions": {"NOTE": "", "2019": -114, "2018": -84}, "Usage": {"NOTE": "", "2019": 103, "2018": 91}, "Balance, December 31": {"NOTE": 10, "2019": -62, "2018": -51}}
usage_2019 = df["Usage"]["2019"]
usage_2018 = df["Usage"]["2018"]
answer = usage_2019 - usage_2018