A copy of "comics" is 3.9 yuan, which is 7.5 yuan more than a copy of "Underwater World". How much is a copy of "Underwater World"?
一本《连环画》3.9元，比一本《海底世界)使宜7.5元．一本《海底世界》多少钱？
<gadget id="calculator">3.9 + 7.5</gadget>
<output>11.4</output>

<result>11.4</result>