The fourth and fifth grades will plant 320 trees. There are 3 classes in the fourth grade, and 40 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320棵树．四年级有3个班，每班栽40棵．剩下的分给五年级4个班栽，平均每班栽多少棵？
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">320 - 120</gadget>
<output>200</output>

<gadget id="calculator">200 / 4</gadget>
<output>50</output>

<result>50</result>