What was the percentage change in operating income between 2017 and 2018?
{"Total operating revenues": {"2018": 127625, "2017": "\u2014", "Change": 127625, "% Change": 100}, "Vessel operating expenses": {"2018": -26317, "2017": -2, "Change": -26315, "% Change": 1315750}, "Voyage expenses": {"2018": -1363, "2017": -121, "Change": -1242, "% Change": 1026}, "Administrative expenses": {"2018": 175, "2017": -1736, "Change": 1911, "% Change": -110}, "Project development expenses": {"2018": -16526, "2017": -2506, "Change": -14020, "% Change": 559}, "Depreciation and amortization": {"2018": -28193, "2017": "\u2014", "Change": -28193, "% Change": 100}, "Other operating gains": {"2018": 2749, "2017": 15100, "Change": -12351, "% Change": -82}, "Operating income": {"2018": 58150, "2017": 10735, "Change": 47415, "% Change": 442}, "Equity in net losses of affiliates": {"2018": -2047, "2017": -8153, "Change": 6106, "% Change": -75}}
operating_income_2018 = df["Operating income"]["2018"]
operating_income_2017 = df["Operating income"]["2017"]
answer = ( operating_income_2018 - operating_income_2017 ) / operating_income_2017 * 100.0