1 watermelon can be exchanged for 4 pears, 2 pears can be exchanged for 3 apples, and how many apples can be exchanged for 2 watermelons.
1个西瓜能换4个梨，2个梨能换3个苹果，2个西瓜能换多少个苹果．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<result>12</result>