Shopping malls have a National Day promotion on October 1. Each box of soap is 14 yuan. If you buy 5 boxes at one time, you will get 2 boxes. Grandma bought 5 boxes at a time. How much is each box cheaper?
商场十一国庆节促销，香皂每盒14元，一次性买5盒就送2盒，奶奶一次买了5盒，每盒便宜多少钱？
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">14 * (5/7)</gadget>
<output>10</output>

<gadget id="calculator">14 - 10</gadget>
<output>4</output>

<result>4</result>