Teacher Li bought several pens, paid 100 yuan, and got back 34 yuan. 16.5 yuan per pen. How many pens did Mr. Li buy?
李老师买了几支钢笔，付了100元，找回34元．每支钢笔16.5元．李老师买了多少支钢笔？
<gadget id="calculator">100 - 34</gadget>
<output>66</output>

<gadget id="calculator">66 / 16.5</gadget>
<output>4</output>

<result>4</result>