Xiaoxiao went to the stationery store and bought an exercise book for 3 yuan, and 4 pens for 28 yuan. How much is an exercise book cheaper than a pen?
笑笑去文具店买了一本练习本用了3元，4支钢笔用了28元，一本练习本比一支钢笔便宜多少元？
<gadget id="calculator">28 / 4</gadget>
<output>7</output>

<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<result>4</result>