There are 12 bicycles and tricycles with 31 wheels. How many bicycles are there?
自行车和三轮车共12辆，有31个轮子，自行车有多少辆．
<gadget id="calculator">3 * 12</gadget>
<output>36</output>

<gadget id="calculator">36 - 31</gadget>
<output>5</output>

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

<gadget id="calculator">5 / 1</gadget>
<output>5</output>

<result>5</result>