According to the statistics of the school library, the average class of the third grade borrows 63 books, and the average class of the fourth grade borrows 77 books. There are 6 classes in each of the two grades. How many books did the third and fourth grade borrow in total?
根据学校图书馆统计，三年级平均每班借阅图书63本，四年级平均每班借阅图书77本，两个年级各有6个班级．三、四年级一共借阅图书多少本？
<gadget id="calculator">63 * 6</gadget>
<output>378</output>

<gadget id="calculator">77 * 6</gadget>
<output>462</output>

<gadget id="calculator">378 + 462</gadget>
<output>840</output>

<result>840</result>