What was the percentage change in total subscription revenue for 2018-2017? 
{"Digital Media": {"2019": 7208.3, "2018": 5857.7, "2017": 4480.8, "% Change 2019 - 2018": 23.0}, "Digital Experience": {"2019": 2670.7, "2018": 1949.3, "2017": 1552.5, "% Change 2019 - 2018": 37.0}, "Publishing": {"2019": 115.5, "2018": 115.2, "2017": 100.6, "% Change 2019 - 2018": "*"}, "Total subscription revenue": {"2019": 9994.5, "2018": 7922.2, "2017": 6133.9, "% Change 2019 - 2018": 26.0}}
total_subscription_revenue_2018 = df["Total subscription revenue"]["2018"]
total_subscription_revenue_2017 = df["Total subscription revenue"]["2017"]
answer = (total_subscription_revenue_2018 - total_subscription_revenue_2017) / total_subscription_revenue_2017 * 100.0