The fourth grade students performed group gymnastics. They were originally arranged in 28 rows, with 15 people standing in each row. After the formation is changed, 20 people stand in each row, how many rows should they stand in?
四年级同学表演团体操，原来排成28列，每列站15人．队形变化后，每列站20人，要站多少列？
<gadget id="calculator">28 / 20</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">15 * (7/5)</gadget>
<output>21</output>

<result>21</result>