What is the increase/ (decrease) in income from December 31, 2018 to 2019?
{"Income": {"Year ended December 31, 2019": 55, "Year ended December 31, 2018": 47, "Year ended December 31, 2017": 30}, "Expense": {"Year ended December 31, 2019": -54, "Year ended December 31, 2018": -54, "Year ended December 31, 2017": -52}, "Total": {"Year ended December 31, 2019": 1, "Year ended December 31, 2018": -7, "Year ended December 31, 2017": -22}}
income_2019 = df["Income"]["Year ended December 31, 2019"]
income_2018 = df["Income"]["Year ended December 31, 2018"]
answer = income_2019 - income_2018