15 students watered the saplings, with an average of 7 trees per person. At this time, a few more students came. Everyone reassigned the tasks, and each person watered 5 trees on average. How many students came again?
15个学生给树苗浇水，平均每人要浇7棵，这时又来了几个同学，大家重新分配任务，平均每人浇5棵，又来了几个同学？
<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<gadget id="calculator">105 / 5</gadget>
<output>21</output>

<gadget id="calculator">21 - 15</gadget>
<output>6</output>

<result>6</result>