Chickens and rabbits are in the same cage, counting 70 feet, counting 20 heads, how many chickens are there?
鸡兔同笼，数脚70只，数头20只，鸡有多少只．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">70 - 40</gadget>
<output>30</output>

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

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<result>5</result>