The students went to plant trees, planting 20 trees in each row, exactly 18 rows. If you plant 9 rows, how many trees are planted in each row?
同学们去种树，每行种20棵，刚好种18行．如果种9行，每行种多少棵？
<gadget id="calculator">18 / 9</gadget>
<output>2</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>