Teacher Ding bought 9 fountain pens and 9 ballpoint pens. The pens cost 270 yuan and the ballpoint pens cost 5 yuan each. How much is each fountain pen more expensive than each ballpoint pen? (calculate with comprehensive formula)
丁老师买了9枝钢笔和9枝圆珠笔，钢笔共用去270元，圆珠笔每支5元．每枝钢笔比每枝圆珠笔贵多少元？(用综合算式计算)
<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<gadget id="calculator">270 - 45</gadget>
<output>225</output>

<gadget id="calculator">225 / 9</gadget>
<output>25</output>

<gadget id="calculator">25 - 5</gadget>
<output>20</output>

<result>20</result>