Each sapling is 16 yuan, buy 3 and get 1 free, buy 3 at a time, how much is each sapling cheaper?
每棵树苗16元，买3棵送1棵，一次买3棵，每棵便宜多少元？
<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">16 * (3/4)</gadget>
<output>12</output>

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

<result>4</result>