Yang Yang buys x boxes of chalk, 3.5 yuan per box, and pays 10 yuan, how much should he get back.
阳阳买x盒粉笔，每盒3.5元，付出10元，应找回多少元．
<gadget id="calculator">10 - 3.5</gadget>
<output>6.5</output>

<result>6.5</result>