To build a road, 30% of the total length was repaired on the first day, 40% of the total length was repaired on the second day, and 500 meters more were repaired on the second day than on the first day. How long is this road?
修一段公路，第一天修了全长的30%，第二天修了全长的40%，第二天比第一天多修500米，这段公路有多长？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">500 / (1/10)</gadget>
<output>5_000</output>

<result>5_000</result>