What is the change in Sales Mix of Hardware between 2018 and 2019?
{"Hardware": {"2019": 34965, "2018": 29496, "%Change": 19}, "Software": {"2019": 92988, "2018": 107363, "%Change": -13}, "Services": {"2019": 52288, "2018": 50055, "%Change": 4}, "": {"2019": 180241, "2018": 186914, "%Change": -4}}
hardware_2019 = df["Hardware"]["2019"]
hardware_2018 = df["Hardware"]["2018"]
answer = hardware_2019 - hardware_2018