In March, the students went to the suburbs to plant trees. If 24 trees are planted in each row, exactly 15 rows will be planted. If 4 trees are planted less in each row, how many rows can be planted? (Solve using ratio method)
3月份同学们到郊外植树，如果每行植24棵，正好植15行，若果每行少植4棵，可以植多少行？(用比例方法解答)
<gadget id="calculator">24 * 15</gadget>
<output>360</output>

<gadget id="calculator">24 - 4</gadget>
<output>20</output>

<gadget id="calculator">360 / 20</gadget>
<output>18</output>

<result>18</result>