What is the difference between the Unused lines of credit for 2019 and 2018?
{"Used lines of credit (1)": {"2019": 98.9, "2018": 232.8}, "Unused lines of credit": {"2019": 1245.2, "2018": 1135.3}, "Total available lines of credit(2)": {"2019": 1344.1, "2018": 1368.1}}
unused_lines_of_credit_2019 = df["Unused lines of credit"]["2019"]
unused_lines_of_credit_2018 = df["Unused lines of credit"]["2018"]
answer = unused_lines_of_credit_2019 - unused_lines_of_credit_2018