There are 15 bicycles and tricycles, and there are 36 wheels in total. How many tricycles are there?
自行车和三轮车共15辆，总共有36个轮子，三轮车有多少辆．
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 - 36</gadget>
<output>9</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">9 / 1</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>