What was the change in the Selling, general and administrative expense from 2017 to 2018?
{"Revenue (1)": {"2018": "$\u2014", "2017": 660}, "Cost of revenue (1)": {"2018": -596, "2017": 2252}, "Gross profit (loss)": {"2018": 596, "2017": -1592}, "Operating expenses:    -- Research and development (1)": {"2018": 5251, "2017": 29167}, "Operating expenses:    -- Selling, general and administrative (1)": {"2018": 1560, "2017": 13840}, "Operating expenses:    -- Total operating expenses": {"2018": 6811, "2017": 43007}, "Operating expenses:    -- Loss from discontinued operations (1)": {"2018": -6215, "2017": -44599}, "Operating expenses:    -- Other income (2)": {"2018": "\u2014", "2017": 7500}, "Operating expenses:    -- Gain on sale (2)": {"2018": "\u2014", "2017": 18022}, "Operating expenses:    -- Loss income before income taxes": {"2018": -6215, "2017": -19077}, "Operating expenses:    -- Income tax provision (benefit)": {"2018": "\u2014", "2017": "\u2014"}, "Operating expenses:    -- Loss income from discontinued operations": {"2018": -6215, "2017": -19077}, "Operating expenses:    -- Cash flow used in Operating Activities (1)": {"2018": -10734, "2017": -42776}, "Operating expenses:    -- Cash flow from Investing Activities (2)": {"2018": "\u2014", "2017": 25522}}
selling_2018 = df["Operating expenses:    -- Selling, general and administrative (1)"]["2018"]
selling_2017 = df["Operating expenses:    -- Selling, general and administrative (1)"]["2017"]
answer = selling_2018 - selling_2017