Mom gave Xiaolan 90 yuan. Xiaolan spent 36 yuan on books, and the remaining money just bought 3 pens. How much is each pen?
妈妈给了小兰90元钱．小兰买书花了36元，剩下的钱正好买了3支钢笔．每支钢笔多少钱？
<gadget id="calculator">90 - 36</gadget>
<output>54</output>

<gadget id="calculator">54 / 3</gadget>
<output>18</output>

<result>18</result>