The fourth and fifth grades will plant 240 trees. There are 3 classes in the fourth grade, and 28 trees are planted in each class. The rest are distributed to the 4 classes of the fifth grade. How many trees are planted in each class on average?
四、五年级要栽240棵树．四年级有3个班，每班栽28棵．剩下的分给五年级的4个班，平均每班栽多少棵？
<gadget id="calculator">28 * 3</gadget>
<output>84</output>

<gadget id="calculator">240 - 84</gadget>
<output>156</output>

<gadget id="calculator">156 / 4</gadget>
<output>39</output>

<result>39</result>