Each notebook is 3.5 yuan, and Xiaohong has 8.4 yuan. She bought a notebook, how much money is left?
笔记本每本3.5元，小红有8.4元，她买了一本笔记本，还剩多少钱？
<gadget id="calculator">8.4 - 3.5</gadget>
<output>4.9</output>

<result>4.9</result>