There are 6 classes in the third and fourth grades of the school, with an average of 55 students in each class of the third grade and 57 students in each class of the fourth grade. How many students are there in the third and fourth grades?
学校三、四年级都有6个班，三年级平均每班55人，四年级平均每班57人．三、四年级共有多少人？
<gadget id="calculator">55 * 6</gadget>
<output>330</output>

<gadget id="calculator">57 * 6</gadget>
<output>342</output>

<gadget id="calculator">330 + 342</gadget>
<output>672</output>

<result>672</result>