Xiaodong took 5 yuan to the store to help his mother buy soy sauce. He saw that a bottle of soy sauce was priced at 3.5 yuan. He asked the salesperson, "Can I get a refund for an empty bottle?" The salesperson replied, "Of course." Soy sauce is 3 yuan more expensive than the bottle. , please help Xiaodong do the math, how much can I get back for an empty bottle?
小东拿5元钱去商店帮妈妈买酱油，一看定价一瓶酱油3.5元，他问售货员："空瓶可以退钱吗？"售货员回答："当然可以．"酱油比瓶子贵3元钱，请你帮小东算一算，一个空瓶子能退多少钱？
<gadget id="calculator">3.5 - 3</gadget>
<output>0.5</output>

<result>0.5</result>