What is the change in total revenue from 2018 to 2019?
{"Equipment revenue": {"2018": 631504, "2019": 1068645}, "Spares & service revenue": {"2018": 186577, "2019": 215215}, "Total": {"2018": 818081, "2019": 1283860}}
total_2019 = df["Total"]["2019"]
total_2018 = df["Total"]["2018"]
answer = total_2019 - total_2018