The school buys 20 pens and 30 pencils and awards them to the good students, and pays a total of 33.3 yuan. Later, the 30 pencils were replaced with 5 pens, and another 4.2 yuan was paid. How much is each pen?
学校购买20支钢笔和30支铅笔奖给三好生，共付33.3元．后来又将30支铅笔换成5支钢笔，又付4.2元，钢笔每支多少？
<gadget id="calculator">33.3 + 4.2</gadget>
<output>37.5</output>

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

<gadget id="calculator">37.5 / 25</gadget>
<output>1.5</output>

<result>1.5</result>