Xiaohong's family ordered 2 bags of fresh milk every day in October (31 days), and paid a total of 173.6 yuan at the preferential price. How much is the preferential price per bag of this fresh milk?
小红家10月份(31天)每天预定2袋鲜牛奶，按优惠价共付了173.6元．这种鲜牛奶每袋优惠价多少元？
<gadget id="calculator">173.6 / 31 / 2</gadget>
<output>2.8</output>

<result>2.8</result>