A thermos bottle is 10.8 yuan, which is 7.7 yuan cheaper than a thermos bottle. How much is a hot water bottle?
一个保温瓶10.8元，比热水瓶便宜7.7元．一个热水瓶多少元？
<gadget id="calculator">10.8 + 7.7</gadget>
<output>18.5</output>

<result>18.5</result>