The original plan was for 18 people to plant trees. After working for 2 hours as planned, 3 people were taken away, so the remaining people planted 1 tree more per hour than the original plan, and they still completed the task on schedule. How many trees were originally planned to be planted per person per hour?
原计划18个人植树，按计划工作了2小时后，有3个人被抽走了，于是剩下的人每小时比原计划多种1棵树，还是按期完成了任务．原计划每人每小时植多少棵树？
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<result>5</result>