To build a 420-meter road, 80 meters per day, and after 4 days of repairing, the rest will be repaired by 20 meters per day, and the rest will be completed in a few days? (Column comprehensive formula solution)
修一段420米的公路，每天修80米，修了4天后剩下的每天多修20米，剩下的几天修完？(列综合算式解答)
<gadget id="calculator">80 * 4</gadget>
<output>320</output>

<gadget id="calculator">420 - 320</gadget>
<output>100</output>

<gadget id="calculator">80 + 20</gadget>
<output>100</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<result>1</result>