There are 3 classes in the third grade of Sunshine Primary School, and each class has 42 students. They plant trees on Arbor Day, and each person plants 3 trees. How many trees are planted in total in the third grade?
阳光小学三年级有3个班，每班有学生42人，植树节他们去植树，每人植树3棵，三年级一共植树多少棵？
<gadget id="calculator">42 * 3 * 3</gadget>
<output>378</output>

<result>378</result>