What was the change in technical maintenance expenses from 2017 to 2018?
{"Crew wages and vessel management employee costs": {"2017": 72652, "2018": 79624, "2019": 80713}, "Technical maintenance expenses": {"2017": 28736, "2018": 28694, "2019": 37653}, "Other vessel operating expenses": {"2017": 21098, "2018": 19766, "2019": 21296}, "Total": {"2017": 122486, "2018": 128084, "2019": 139662}}
technical_maintenance_expenses_2018 = df["Technical maintenance expenses"]["2018"]
technical_maintenance_expenses_2017 = df["Technical maintenance expenses"]["2017"]
answer = technical_maintenance_expenses_2018 - technical_maintenance_expenses_2017