In Hongxing Primary School’s book donation activity for poverty alleviation, male students donated an average of 12 books, and female students donated an average of 9 books. The number of female students was twice the number of male students. In this activity, how many books are donated by each student in the school on average.
红星小学在扶贫捐书的活动中，男同学平均每人捐书12本，女同学平均每人捐书9本，女同学的人数是男同学人数的2倍．这次活动中该校平均每位同学捐书多少本．
<gadget id="calculator">12 * 1</gadget>
<output>12</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<result>10</result>