What was the percentage change in the CO2 emissions amount in London in 2019 from 2018?
{"Scope 1": {"FY19": 263.0, "FY18": 390.0, "FY17": 491.0, "FY16": 565.0}, "Manchester": {"FY19": 213.0, "FY18": 281.0, "FY17": 361.0, "FY16": 357.0}, "London": {"FY19": 44.0, "FY18": 60.0, "FY17": 76.0, "FY16": 88.0}, "Scope 2": {"FY19": 258.0, "FY18": 340.0, "FY17": 437.0, "FY16": 445.0}, "Total": {"FY19": 521.0, "FY18": 731.0, "FY17": 928.0, "FY16": 1010.0}, "Revenue": {"FY19": 355.1, "FY18": 330.1, "FY17": 311.5, "FY16": 281.6}, "Carbon intensity": {"FY19": 1.47, "FY18": 2.21, "FY17": 2.98, "FY16": 3.59}, "Year-on-year change": {"FY19": -34.0, "FY18": -26.0, "FY17": -17.0, "FY16": ""}}
london_fy19 = df["London"]["FY19"]
london_fy18 = df["London"]["FY18"]
answer = ( london_fy19 - london_fy18 ) / london_fy18 * 100.0