Chickens and rabbits are in the same cage, with a total of 15 heads and 50 feet. Then how many chickens are there?
鸡、兔同笼，共有15个头，50只脚．则鸡有多少只．
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">60 - 50</gadget>
<output>10</output>

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

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<result>5</result>