What was the percentage change in operating expenses between 2018 and 2019?
{"Revenues": {"2019 (1)": 59.5, "2018": 57.6, "2017": 56.8}, "Operating expenses": {"2019 (1)": 12.5, "2018": 12.1, "2017": 12.3}, "Guarantee fee": {"2019 (1)": "\u2014", "2018": "\u2014", "2017": 1.2}}
operating_expenses_2019 = df["Operating expenses"]["2019 (1)"]
operating_expenses_2018 = df["Operating expenses"]["2018"]
answer = ( operating_expenses_2019 - operating_expenses_2018 ) / operating_expenses_2018 * 100.0