Mr. Wang bought 20 pens and 30 pencils to reward advanced students. He paid a total of 45 yuan. Later, he changed the 30 pencils into 5 pens and paid another 5 yuan. Do you know how much each pen costs?
王老师购买了20支钢笔和30支铅笔奖励进步生，共付出45元，后来将30支铅笔换成5支钢笔并又付了5元，你知道每支钢笔多少钱吗？
<gadget id="calculator">45 + 5</gadget>
<output>50</output>

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

<gadget id="calculator">50 / 25</gadget>
<output>2</output>

<result>2</result>