There are 10 bicycles and tricycles with a total of 28 wheels. How many bicycles are there?
自行车和三轮车共10辆，总共有28个轮子．自行车有多少辆．
<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">30 - 28</gadget>
<output>2</output>

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

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

<result>2</result>