What was the change in the revenues from Aerospace & Defense between 2018 and 2019?
{"Transportation": {"2019": 299005, "2018": 300124}, "Industrial": {"2019": 78369, "2018": 86968}, "Medical": {"2019": 41901, "2018": 40663}, "Aerospace & Defense": {"2019": 32569, "2018": 23323}, "Telecom & IT": {"2019": 17155, "2018": 19405}, "Total": {"2019": 468999, "2018": 470483}}
aerospace_defense_2019 = df["Aerospace & Defense"]["2019"]
aerospace_defense_2018 = df["Aerospace & Defense"]["2018"]
answer = aerospace_defense_2019 - aerospace_defense_2018