What is the change in Sales Mix of Software between 2018 and 2019?
{"Hardware": {"2019": 3957507, "2018": 3610356, "%Change": 10}, "Software": {"2019": 1269983, "2018": 1112715, "%Change": 14}, "Services": {"2019": 796815, "2018": 639910, "%Change": 25}, "": {"2019": 6024305, "2018": 5362981, "%Change": 12}}
software_2019 = df["Software"]["2019"]
software_2018 = df["Software"]["2018"]
answer = software_2019 - software_2018