What is the percentage change in the voyage revenue between 2018 and 2019?
{"Voyage Revenue  ": {"2019": 317220.0, "2018": 289016.0, "Variance ": 9.8}, "Voyage Expenses  ": {"2019": -141770.0, "2018": -165012.0, "Variance ": -14.1}, "Vessel Operating Expenses  ": {"2019": -66033.0, "2018": -80411.0, "Variance ": -17.9}, "Impairment Loss on Vessels  ": {"2019": "-", "2018": -2168, "Variance ": "N/A "}, "Impairment Loss on Goodwill  ": {"2019": "-", "2018": "-", "Variance ": "N/A "}, "Loss from Disposal of Vessels  ": {"2019": "-", "2018": -6619, "Variance ": "N/A "}, "General and Administrative Expenses  ": {"2019": -13481.0, "2018": -12727.0, "Variance ": 5.9}, "Depreciation Expenses  ": {"2019": -63965.0, "2018": -60695.0, "Variance ": 5.4}, "Net Operating (Loss) Income  ": {"2019": 31971.0, "2018": -38616.0, "Variance ": -182.8}, "Interest Income  ": {"2019": 298.0, "2018": 334.0, "Variance ": -10.8}, "Interest Expenses  ": {"2019": -38390.0, "2018": -34549.0, "Variance ": 11.1}, "Other Financial Expenses  ": {"2019": -4231.0, "2018": -14808.0, "Variance ": -71.4}, "Equity Loss from Associate  ": {"2019": "-", "2018": -7667, "Variance ": "N/A "}, "Net (Loss) Income  ": {"2019": -10352.0, "2018": -95306.0, "Variance ": -89.1}}
voyage_revenue_2019 = df["Voyage Revenue  "]["2019"]
voyage_revenue_2018 = df["Voyage Revenue  "]["2018"]
answer = ( voyage_revenue_2019 - voyage_revenue_2018 ) / voyage_revenue_2018 * 100.0