In the school planting, 84 trees were planted in the fourth grade, which is twice the number of trees planted in the third grade. How many trees were planted in the third and fourth grades?
学校植树，四年级植树84棵，是三年级植树的2倍，三四年级一共植树多少棵？
<gadget id="calculator">84 / 2</gadget>
<output>42</output>

<gadget id="calculator">42 + 84</gadget>
<output>126</output>

<result>126</result>