What was the difference in the variance in dollars between Available-for-sale debt investments and net Other gains (losses)?
{"Gains (losses) on investments, net: -- Available-for-sale debt investments": {"July 27, 2019": -13, "July 28, 2018": -242, "July 29, 2017": -42, "Variance in Dollars": 229}, "Gains (losses) on investments, net: -- Marketable equity investments": {"July 27, 2019": -3, "July 28, 2018": 529, "July 29, 2017": -45, "Variance in Dollars": -532}, "Gains (losses) on investments, net: -- Non-marketable equity and other investments": {"July 27, 2019": 6, "July 28, 2018": 11, "July 29, 2017": -46, "Variance in Dollars": -5}, "Gains (losses) on investments, net: -- Net gains (losses) on investments": {"July 27, 2019": -10, "July 28, 2018": 298, "July 29, 2017": -133, "Variance in Dollars": -308}, "Gains (losses) on investments, net: -- Other gains (losses), net": {"July 27, 2019": -87, "July 28, 2018": -133, "July 29, 2017": -30, "Variance in Dollars": 46}, "Gains (losses) on investments, net: -- Other income (loss), net": {"July 27, 2019": -97, "July 28, 2018": 165, "July 29, 2017": -163, "Variance in Dollars": -262}}
var_available_for_sale = df["Gains (losses) on investments, net: -- Available-for-sale debt investments"]["Variance in Dollars"]
var_other_gains_losses = df["Gains (losses) on investments, net: -- Other gains (losses), net"]["Variance in Dollars"]
answer = var_available_for_sale - var_other_gains_losses