The stationery store launched a "buy three get one free" campaign. If a pen originally sold for 12 yuan, and Xiaohong bought 3 pens at a time, how much is each pen cheaper?
文具店开展"买三赠一"的活动，如果原来一支笔卖12元，小红一次买3支，每支便宜了多少元．
<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>