On Sunday, "Jiajiale Supermarket" is doing promotional activities. Washing powder is 12.00 yuan per bag, buy 3 bags and get 1 bag free, mom bought 3 bags at a time, how much is each bag cheaper than before the promotion?
星期天，"家家乐超市"搞促销活动．洗衣粉每袋12.00元，买3袋送一袋，妈妈一次买了3袋，每袋比促销活动前便宜多少元？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">12 * (3/4)</gadget>
<output>9</output>

<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<result>3</result>