What is the change in U.S. build-to-suit facility from March 31, 2018 to March 31, 2019?
{"U.S. build-to-suit facility": {"2019": 47001, "2018": 43925}, "U.K. build-to-suit facility": {"2019": "\u2014", "2018": 31240}, "Less: Accumulated depreciation": {"2019": -5164, "2018": -753}, "": {"2019": 41837, "2018": 74412}}
us_buildtosuit_facility_2019 = df["U.S. build-to-suit facility"]["2019"]
us_buildtosuit_facility_2018 = df["U.S. build-to-suit facility"]["2018"]
answer = us_buildtosuit_facility_2019 - us_buildtosuit_facility_2018