What was the change in balance from Americas between 2018 and 2019?
{"Americas": {"Balance at July 28, 2018": 19998, "Acquisitions & Divestitures": 1240, "Other": -118, "Balance at July 27, 2019": 21120}, "EMEA": {"Balance at July 28, 2018": 7529, "Acquisitions & Divestitures": 486, "Other": -38, "Balance at July 27, 2019": 7977}, "APJC": {"Balance at July 28, 2018": 4179, "Acquisitions & Divestitures": 274, "Other": -21, "Balance at July 27, 2019": 4432}, "Total": {"Balance at July 28, 2018": 31706, "Acquisitions & Divestitures": 2000, "Other": -177, "Balance at July 27, 2019": 33529}}
americas_balance_at_july_27_2019 = df["Americas"]["Balance at July 27, 2019"]
americas_balance_at_july_28_2018 = df["Americas"]["Balance at July 28, 2018"]
answer = americas_balance_at_july_27_2019 - americas_balance_at_july_28_2018