The fourth and fifth graders of Guangming Elementary School planted 340 trees together, and the fifth graders worked for 4 hours, planting 50 trees per hour. The fourth grade students worked for 5 hours, how many trees were planted per hour on average?
光明小学四年级和五年级同学一起种树，共种了340棵，五年级同学劳动了4时，每时种树50棵．四年级同学劳动了5时，平均每时种树多少棵？
<gadget id="calculator">50 * 4</gadget>
<output>200</output>

<gadget id="calculator">340 - 200</gadget>
<output>140</output>

<gadget id="calculator">140 / 5</gadget>
<output>28</output>

<result>28</result>