A certain school greened the campus and planted 3 rows of poplars and 15 willows. A total of 39 trees were planted. How many poplars are there in each row?
某校绿化校园，栽了3行杨树，15棵柳树，一共栽了39棵树，每行杨树多少棵？
<gadget id="calculator">39 - 15</gadget>
<output>24</output>

<gadget id="calculator">24 / 3</gadget>
<output>8</output>

<result>8</result>