What is the percentage change in net sales from 2018 to 2019?
{"Net sales": {"2019": 245862.0, "2018": 193237.0, "2017": 152359.0, "2016": 129707.0, "2015": 113505.0}, "Cost of goods sold": {"2019": 131665.0, "2018": 103247.0, "2017": 79943.0, "2016": 69336.0, "2015": 58856.0}, "Gross profit": {"2019": 114197.0, "2018": 89990.0, "2017": 72416.0, "2016": 60371.0, "2015": 54649.0}, "Selling, general and administrative expenses": {"2019": 114450.0, "2018": 94876.0, "2017": 75167.0, "2016": 62586.0, "2015": 58297.0}, "Loss from operations": {"2019": -253.0, "2018": -4886.0, "2017": -2751.0, "2016": -2215.0, "2015": -3648.0}, "Other income (expenses), net": {"2019": 5.0, "2018": -102.0, "2017": -525.0, "2016": -182.0, "2015": 449.0}, "Interest expense": {"2019": -991.0, "2018": -296.0, "2017": -910.0, "2016": -698.0, "2015": -455.0}, "Loss before income taxes": {"2019": -1239.0, "2018": -5284.0, "2017": -4187.0, "2016": -3095.0, "2015": -3653.0}, "Income tax expense": {"2019": 144.0, "2018": 77.0, "2017": 75.0, "2016": 66.0, "2015": 58.0}, "Net loss attributable to common stockholders": {"2019": -1383.0, "2018": -5361.0, "2017": -4262.0, "2016": -3161.0, "2015": -3711.0}, "Net loss per share -- Basic": {"2019": -0.04, "2018": -0.15, "2017": -0.12, "2016": -0.09, "2015": -0.11}, "Net loss per share -- Diluted": {"2019": -0.04, "2018": -0.15, "2017": -0.12, "2016": -0.09, "2015": -0.11}, "Weighted Average shares of common stock outstanding -- Basic": {"2019": 35950117.0, "2018": 35329170.0, "2017": 34487239.0, "2016": 33674416.0, "2015": 33497940.0}, "Weighted Average shares of common stock outstanding -- Diluted": {"2019": 35950117.0, "2018": 35329170.0, "2017": 34487239.0, "2016": 33674416.0, "2015": 33497940.0}}
net_sales_2019 = df["Net sales"]["2019"]
net_sales_2018 = df["Net sales"]["2018"]
answer = (net_sales_2019 - net_sales_2018) / net_sales_2018 * 100.0