If: 2 sheep = 1 pig, 4 pigs = 1 cow. So, 2 cows = how many sheep.
如果：2只羊=1头猪，4头猪=1头牛．那么，2头牛=多少只羊．
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">2 * 8</gadget>
<output>16</output>

<result>16</result>