For school tree planting, 84 trees were planted in the fourth grade, twice that of the third grade. The number of trees planted in the fifth grade was the sum of the trees planted in the third and fourth grades. How many trees were planted in the fifth grade?
学校植树，四年级植树84棵，是三年级植树的2倍，五年级植树的棵数是三、四两个年级植树的总和，五年级植树多少棵？
<gadget id="calculator">84 / 2</gadget>
<output>42</output>

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

<result>126</result>