Xiaohong brought 10 yuan and bought a ballpoint pen, leaving 6.4 yuan. How much is this ballpoint pen?
小红带了10元，买了一支圆珠笔，剩下6.4元．这支圆珠笔多少钱？
<gadget id="calculator">10 - 6.4</gadget>
<output>3.6</output>

<result>3.6</result>