What was the change in the Net sales between the Dec-31 and Mar-31 quarters?
{"Fiscal Year 2019 Quarters Ended -- ": {"Jun-30": -30.0, "Sep-30": -30.0, "Dec-31": -31.0, "Mar-31": -31.0}, "Fiscal Year 2019 Quarters Ended -- Net sales": {"Jun-30": 327616.0, "Sep-30": 349233.0, "Dec-31": 350175.0, "Mar-31": 355794.0}, "Fiscal Year 2019 Quarters Ended -- Gross margin": {"Jun-30": 94821.0, "Sep-30": 113565.0, "Dec-31": 123750.0, "Mar-31": 126406.0}, "Fiscal Year 2019 Quarters Ended -- Operating income (1)": {"Jun-30": 35176.0, "Sep-30": 50000.0, "Dec-31": 61616.0, "Mar-31": 54057.0}, "Fiscal Year 2019 Quarters Ended -- Net income": {"Jun-30": 35220.0, "Sep-30": 37141.0, "Dec-31": 40806.0, "Mar-31": 93420.0}, "Fiscal Year 2019 Quarters Ended -- Net income per basic share": {"Jun-30": 0.61, "Sep-30": 0.64, "Dec-31": 0.7, "Mar-31": 1.6}, "Fiscal Year 2019 Quarters Ended -- Net income per diluted share": {"Jun-30": 0.6, "Sep-30": 0.63, "Dec-31": 0.69, "Mar-31": 1.58}}
net_sales_mar31 = df["Fiscal Year 2019 Quarters Ended -- Net sales"]["Mar-31"]
net_sales_dec31 = df["Fiscal Year 2019 Quarters Ended -- Net sales"]["Dec-31"]
answer = net_sales_mar31 - net_sales_dec31