Each sapling is 36 yuan, buy 3 and get 1 free. If you buy 3 trees at a time, how much is it actually cheaper for each tree?
每棵树苗36元，买3棵送1棵．如果一次买3棵，实际每棵便宜多少元？
<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">36 * (3/4)</gadget>
<output>27</output>

<gadget id="calculator">36 - 27</gadget>
<output>9</output>

<result>9</result>