Use 216 yuan to buy a pen, and the money is just used up. If each pen is 1 yuan cheaper, you can buy 3 more pens, and the money is just used up. How many pens did you buy?
用216元去买一种钢笔，正好将钱用完，如果每支钢笔便宜1元，则可以多买3支钢笔，钱也正好用完，问买了多少支钢笔？
<gadget id="calculator">216 / 9</gadget>
<output>24</output>

<result>24</result>