Wang Hua spent 50 yuan to buy 12 exercise books, 1.8 yuan each, and bought 4 pens with the remaining money. How much is each pen?
王华用50元买了12本练习本，每本1.8元，剩下的钱买了4枝钢笔，钢笔每枝多少元？
<gadget id="calculator">12 * 1.8</gadget>
<output>21.6</output>

<gadget id="calculator">50 - 21.6</gadget>
<output>28.4</output>

<gadget id="calculator">28.4 / 4</gadget>
<output>7.1</output>

<result>7.1</result>