Xiaoli's chickens and rabbits are in the same cage. There are 10 heads on the top and 28 feet on the bottom. How many chickens are there?
小丽家鸡、兔同笼．上有10只头，下有28只脚，鸡有多少只．
<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<result>6</result>