A road construction team builds a road, originally planned to build 1.5 kilometers per day, and completed it in 28 days, but actually built 2.1 kilometers per day. How many days did it actually take? (Solve with ratio)
一个筑路队修一条公路，原计划每天修1.5千米，28天完成，实际每天修2.1千米．实际修了多少天？(用比例解)
<gadget id="calculator">1.5 * 28</gadget>
<output>42</output>

<gadget id="calculator">42 / 2.1</gadget>
<output>20</output>

<result>20</result>