Xiaohong bought two fountain pens and a ballpoint pen for 16 yuan, and she bought another fountain pen and two ballpoint pens for 11 yuan. How much is a pen?
小红买了两支钢笔和一支圆珠笔共用去16元，她又买了一支钢笔和两支圆珠笔共用去11元，一支钢笔多少元．
<gadget id="calculator">16 * 2</gadget>
<output>32</output>

<gadget id="calculator">32 - 11</gadget>
<output>21</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">21 / 3</gadget>
<output>7</output>

<result>7</result>