There are 4 classes in the third grade, each class has 42 students, and each person plants 4 trees on average. How many trees did the third graders plant in total?
三年级有4个班，每班有学生42人，平均每人植树4棵．三年级学生一共植树多少棵？
<gadget id="calculator">42 * 4 * 4</gadget>
<output>672</output>

<result>672</result>