1 chicken for 2 rabbits, 1 goose for 2 chickens, 2 geese for how many rabbits.
1只鸡换2只兔，1只鹅换2只鸡，2只鹅换多少只兔．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

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

<result>8</result>