Xiaohong brought 100 yuan and bought 9 ballpoint pens, leaving 64 yuan. How much is a ballpoint pen?
小红带了100元，买了9支圆珠笔，剩下64元．一支圆珠笔多少钱？
<gadget id="calculator">100 - 64</gadget>
<output>36</output>

<gadget id="calculator">36 / 9</gadget>
<output>4</output>

<result>4</result>