What was the change in assets from U.S. property between 2018 and 2019?
{"U.S. property": {"2019 (1)": 22624.6, "2018": 18782.0, "2017": 19032.6}, "Asia property (2)": {"2019 (1)": 5307.8, "2018": 4938.8, "2017": 4770.8}, "Africa property (2)": {"2019 (1)": 4711.1, "2018": 1929.7, "2017": 1673.4}, "Europe property (2)": {"2019 (1)": 1535.3, "2018": 1438.1, "2017": 1540.2}, "Latin America property (2)": {"2019 (1)": 8125.5, "2018": 5594.7, "2017": 5868.4}, "Services": {"2019 (1)": 26.8, "2018": 46.3, "2017": 42.3}, "Other (3)": {"2019 (1)": 470.5, "2018": 280.8, "2017": 286.6}, "Total assets": {"2019 (1)": 42801.6, "2018": 33010.4, "2017": 33214.3}}
us_property_2019_1 = df["U.S. property"]["2019 (1)"]
us_property_2018 = df["U.S. property"]["2018"]
answer = us_property_2019_1 - us_property_2018