There are two books in the bookstore, "Selected Fairy Tales" is 6.8 yuan each, and "Use Your Brain" is 3.5 yuan each. How much cheaper is "Use Your Brain" than "Selected Fairy Tales"?
书店有两本书，《童话故事选》每本6.8元，《动脑筋》每本3.5元，《动脑筋》比《童话故事选》便宜多少元？
<gadget id="calculator">6.8 - 3.5</gadget>
<output>3.3</output>

<result>3.3</result>