What is the change in revenues from ASG from 2018 to 2019?
{"PSG": {"2019": 2788.3, "2018": 3038.2}, "ASG": {"2019": 1972.3, "2018": 2071.2}, "ISG": {"2019": 757.3, "2018": 768.9}, "Total revenue": {"2019": 5517.9, "2018": 5878.3}}
asg_2019 = df["ASG"]["2019"]
asg_2018 = df["ASG"]["2018"]
answer = asg_2019 - asg_2018