What was the percentage change in the revenue between 2018 and 2019?
{"Revenue": {"2019": 527550.0, "2018": 451013.0}, "Net income attributable to common stockholders": {"2019": 51075.0, "2018": 13264.0}, "Net income attributable to common stockholders per share - basic": {"2019": 1.05, "2018": 0.27}, "Net income attributable to common stockholders per share - diluted": {"2019": 1.02, "2018": 0.26}}
revenue_2019 = df["Revenue"]["2019"]
revenue_2018 = df["Revenue"]["2018"]
answer = ( revenue_2019 - revenue_2018 ) / revenue_2018 * 100.0