Supermarkets hold promotional activities on the National Day. Want Want gifts are 16 yuan a bag, buy three and get one free. Mom bought three bags, how much can each bag be cheaper?
超市国庆搞促销活动，旺旺礼品装16元一袋，买三送一，妈妈买了三袋，每袋可以便宜多少钱？
<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">16 * (3/4)</gadget>
<output>12</output>

<gadget id="calculator">16 - 12</gadget>
<output>4</output>

<result>4</result>