There are 69 students in class 3 and 5, and each person donates 2 books to the school on average. How many books have they donated in total?
三5班有69人，平均每人向学校捐2本书，一共捐了多少本．
<gadget id="calculator">69 * 2</gadget>
<output>138</output>

<result>138</result>