certain brand of toothpaste is 12 yuan per box, and the supermarket implements a promotional activity to buy 3 and get 1 free. Mom bought 3 boxes at once, how much is each box cheaper?
某品牌牙膏每盒12元，超市实行促销活动买3送1，妈妈一次性买了3盒，每盒便宜多少元？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<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>