In the fourth and fifth grades, 120 trees should be planted. There are 3 classes in the fourth grade, and 28 trees are planted in each class. The rest will be planted in 4 classes of the fifth grade. How many trees will be planted in each class on average?
四、五年级要栽120棵树．四年级有3个班，每班栽28棵．剩下的分给五年级4个班栽，平均每班栽多少棵？
<gadget id="calculator">28 * 3</gadget>
<output>84</output>

<gadget id="calculator">120 - 84</gadget>
<output>36</output>

<gadget id="calculator">36 / 4</gadget>
<output>9</output>

<result>9</result>