Digging a 4,500-meter-long canal, 20% of the total length was dug 4 days before the start of construction. According to this calculation, how many days will it take to complete the road? (Solution with proportional knowledge)
挖一条长4500米的水渠，开工前4天挖了全长的20%米，照这样计算，修完这条路共需多少天？(用比例知识解)
<gadget id="calculator">4 * 4_500</gadget>
<output>18_000</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4_500 * (1/5)</gadget>
<output>900</output>

<gadget id="calculator">18_000 / 900</gadget>
<output>20</output>

<result>20</result>