There are 840 apple trees and peach trees in the orchard, among which there are 15 rows of apple trees, each with 24 trees. If there are 20 rows of peach trees, how many trees are there on average in each row?
果园里有苹果树和桃树共有840棵，其中苹果树有15行，每行24棵．如果桃树有20行，平均每行有多少棵？
<gadget id="calculator">24 * 15</gadget>
<output>360</output>

<gadget id="calculator">840 - 360</gadget>
<output>480</output>

<gadget id="calculator">480 / 20</gadget>
<output>24</output>

<result>24</result>