Chickens and rabbits are in the same cage. There are 42 heads and 130 feet. How many chickens are there?
鸡兔同笼，头有42个，脚有130只，鸡有多少只．
<gadget id="calculator">4 * 42</gadget>
<output>168</output>

<gadget id="calculator">168 - 130</gadget>
<output>38</output>

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

<gadget id="calculator">38 / 2</gadget>
<output>19</output>

<result>19</result>