Two fountain pens and one ballpoint pen total 16 yuan, and one fountain pen and two ballpoint pens total 11 yuan. How much is one fountain pen?
两枝钢笔和一枝圆珠笔共16元，一枝钢笔和两枝圆珠笔共11元，那么一枝钢笔是多少元？
<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>