pencil case is 8.5 yuan, a pen is 3.5 yuan, how much is a pen cheaper than a pencil case?
一个文具盒8.5元，一支钢笔3.5元，一支钢笔比一个文具盒便宜多少钱？
<gadget id="calculator">8.5 - 3.5</gadget>
<output>5</output>

<result>5</result>