Buy 4 notebooks, pay 50 yuan, get back 34 yuan, how much is each notebook.
买4本笔记本，付出50元，找回34元，每本多少元．
<gadget id="calculator">50 - 34</gadget>
<output>16</output>

<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<result>4</result>