There are 3 pen holders with an average of 6 pens in each pen holder. There are 6 pens in the first pen holder, 7 pens in the second pen holder, and how many pens are there in the third pen holder.
3个笔筒平均每个笔筒有6支笔，第1个笔筒里有6支笔，第2个笔筒里有7支笔，第3个笔筒里有多少支笔．
<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">18 - 6 - 7</gadget>
<output>5</output>

<result>5</result>