Teacher Ding bought 9 fountain pens and 9 ballpoint pens, 270 yuan for the pens and 45 yuan for the ballpoint pens. How much is each fountain pen more expensive than each ballpoint pen?
丁老师买了9枝钢笔和9枝圆珠笔，钢笔共用去270元，圆珠笔共用去45元．每枝钢笔比每枝圆珠笔贵多少元？
<gadget id="calculator">270 / 9</gadget>
<output>30</output>

<gadget id="calculator">45 / 9</gadget>
<output>5</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<result>25</result>