What was the percentage change in total voyage expenses and commissions from 2017 to 2018?
{"Brokers commissions on revenue": {"2017": 6456, "2018": 7555, "2019": 7527}, "Bunkers consumption and other voyage expenses": {"2017": 8948, "2018": 12819, "2019": 16245}, "Total": {"2017": 15404, "2018": 20374, "2019": 23772}}
total_2018 = df["Total"]["2018"]
total_2017 = df["Total"]["2017"]
answer = ( total_2018 - total_2017 ) / total_2017 * 100.0