If 1 cow can be exchanged for 3 pigs, and 1 pig can be exchanged for 3 sheep, then how many sheep can be exchanged for 1 cow.
如果1头牛可以换3头猪，1头猪可以换3只羊，那么1头牛可以换多少只羊．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<result>9</result>