A kind of fresh milk, the retail price of each bag is 1.10 yuan. Xiaohua's family ordered 3 bags of this kind of fresh milk every day in April, and paid a total of 85.5 yuan at the preferential price. How much is the preferential price cheaper than the retail price per bag?
一种鲜奶，每袋的零售价是1.10元．小华家四月份每天预定3袋这样的鲜奶，按优惠价共付了85.5元．优惠价每袋比零售价便宜多少元？
<gadget id="calculator">3 * 30</gadget>
<output>90</output>

<gadget id="calculator">85.5 / 90</gadget>
<output>0.95</output>

<gadget id="calculator">1.1 - 0.95</gadget>
<output>0.15</output>

<result>0.15</result>