The third grade participates in the broadcasting exercise competition. There are 18 people in each row, and they need to stand in 21 rows; if there are 9 people in each row, how many rows do they need to stand in?
三年级参加广播操比赛，每排18人，需要站21列；如果每排9人，需要站几列？
<gadget id="calculator">21 / 9</gadget>
<output>7/3 = around 2.333333</output>

<gadget id="calculator">18 * (7/3)</gadget>
<output>42</output>

<result>42</result>