What was the change in the United States net property and equipment between 2019 and 2020?
{"United States": {"January 1, 2020": 860, "February 1, 2019": 849}, "International": {"January 1, 2020": 209, "February 1, 2019": 113}, "Total": {"January 1, 2020": 1069, "February 1, 2019": 962}}
us_january_2020 = df["United States"]["January 1, 2020"]
us_february_2019 = df["United States"]["February 1, 2019"]
answer = us_january_2020 - us_february_2019