Zhao Min went to the store to buy school supplies. If he bought all the exercise books, he could buy 15 books; if he bought all the fountain pens, he could buy 20 pens. Now he buys 6 exercise books first, how many fountain pens can he buy with the remaining money?
赵敏同学去商店买学习用品，所带的钱如果全部买练习本，可以买15本；如果全部买水笔，可以买20支．现在他先买6本练习本，剩下的钱还可以买几支水笔？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 6</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(3/5) / (1/20)</gadget>
<output>12</output>

<result>12</result>