A kind of towel, the price of each towel is 16 yuan, buy 3 and get 1 free. I bought 3 pieces at a time (4 pieces in real time), how much is each piece cheaper?
一种毛巾，每条的价格是16元，买3条送1条．一次买了3条(实得4条)，每条便宜多少钱？
<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>